BMI calculator

What Is a BMI Calculator?

A BMI calculator works out your body mass index, a single number that compares your weight to your height. You enter both measurements, and the tool gives you a figure and tells you which general weight range it falls into: underweight, healthy weight, overweight or obese.

Doctors, nurses, dietitians and public health organisations use BMI because it is quick, free and needs no special equipment. It is a screening tool, which means it points to whether your weight might deserve a closer look. It does not diagnose anything, and it cannot tell you how healthy you are as a person.

This calculator is meant for adults, usually people aged 20 and above. Children and teenagers are assessed differently, and we cover that further down.

What Can You Use a BMI Calculator For?

Most people use it for one of these reasons

• Checking whether their weight is in a range generally considered healthy for their height
• Setting a realistic weight goal before starting to lose or gain weight
• Tracking changes over several months, for example after changing diet or exercise habits
• Preparing for a medical check-up, a fitness programme or a form that asks for BMI
• Understanding a number a clinic or hospital has already mentioned
• Satisfying curiosity after a change in appetite, lifestyle or clothing size

It is also useful for students working on health, biology or nutrition assignments, and for anyone who simply wants a starting point for a conversation with a health professional.

How to Use the BMI Calculator

You do not need any technical knowledge. Use the calculator above this guide and follow these steps:

1. Measure your height. Stand straight against a wall without shoes, with your heels touching the wall, and mark the top of your head. Measure from the floor to the mark.
2. Weigh yourself. Use a scale on a flat, hard surface. For the most consistent readings, weigh yourself in the morning, after using the toilet and before eating, wearing light clothing.
3. Enter your height in the height field. Use the unit the calculator offers, such as centimetres, metres, or feet and inches.
4. Enter your weight in the weight field, in kilograms or pounds depending on the options provided.
5. Press the calculate button.
6. Read your BMI number and the category shown beside it.

If you are unsure of your height, ask someone to measure you properly instead of guessing. A difference of just a few centimetres can shift the result by a noticeable amount.

Understanding the Results

Your result is a number, usually with one decimal place, such as 22.9. The number is then matched to a category. The standard adult ranges used by the World Health Organization are:

A few things are worth understanding about these numbers.

The categories are guidelines, not verdicts. Someone with a BMI of 25.3 is not meaningfully different from someone with 24.8. The lines are drawn for population-level screening, and individual bodies do not switch from healthy to unhealthy at a cut-off point.

BMI measures weight, not fat. The formula cannot tell the difference between fat, muscle, bone and water. That is the single biggest reason BMI can mislead.

A result outside the healthy range is a prompt, not a diagnosis. If your BMI is low or high, it is sensible to look at other signs, such as your waist size, energy levels, blood pressure, blood sugar and family history, ideally with a health professional.

How BMI Is Calculated

The formula is simple enough to check by hand

BMI = weight in kilograms divided by (height in metres × height in metres)

If you use pounds and inches, the formula is

BMI = (weight in pounds × 703) divided by (height in inches × height in inches)

For example, a person who weighs 70 kg and is 1.75 m tall

• Height squared: 1.75 × 1.75 = 3.0625
• BMI: 70 ÷ 3.0625 = 22.9

That puts the person in the healthy weight range.

Practical Examples

These examples show how the calculation works in everyday situations.

Example 1: A young adult checking their weight

Aisha is 1.65 m tall and weighs 52 kg. Her height squared is 2.7225, and 52 ÷ 2.7225 gives a BMI of about 19.1. This is in the healthy range, close to the lower end. If she has been losing weight without trying, or feels tired often, that would be worth mentioning to a doctor even though the number looks fine.

Example 2: Someone who has gained weight over a few years

Musa is 1.68 m tall and now weighs 85 kg. His height squared is 2.8224, so his BMI is about 30.1, which is the start of the obesity range. For him, the number is a reason to look at diet, activity, sleep and blood pressure, and perhaps to speak with a clinician about a sensible, gradual plan.

Example 3: A person who is underweight

Ibrahim is 1.70 m tall and weighs 48 kg. His height squared is 2.89, giving a BMI of about 16.6. This is below the healthy range. Possible causes include not eating enough, illness, stress, or simply a naturally slim build, so a medical check is the right next step instead of guessing.

Example 4: A muscular person

Chidi lifts weights regularly. He is 1.80 m tall and weighs 95 kg. His height squared is 3.24, so his BMI is about 29.3, which falls in the overweight category. But much of his weight may be muscle, so the label may not describe his health at all. Waist measurement and body composition checks would tell a clearer story.

Example 5: Using feet and inches

Fatima is 5 feet 4 inches tall, which is 64 inches, and weighs 140 pounds. The calculation is (140 ? 703) ÷ (64 ? 64) = 98,420 ÷ 4,096, which is about 24.0. That is within the healthy range.

How to Get Better Results

The calculator is only as accurate as the numbers you give it. A few habits make the result more reliable:

• Measure height without shoes. Even thick socks and shoe soles add a little.
• Weigh yourself at a consistent time. Body weight can vary by a kilogram or more across a single day because of food, water and activity.
• Use the same scale each time if you are tracking progress. Different scales can disagree slightly.
• Do not round aggressively. If you are 1.68 m, do not enter 1.7 m. The formula squares your height, so small errors grow.
• Check your units. Entering pounds where kilograms are expected is the most common cause of strange results.
• Look at trends instead of single readings. One result tells you little. A pattern over several months tells you more.
• Combine BMI with other measures. Waist circumference, how your clothes fit, your energy and your medical test results all add context.

Common Problems and How to Fix Them

The result looks far too high or too low

Check that you entered height in the right unit. A height of 170 entered as metres instead of centimetres, or a weight of 150 entered in kilograms instead of pounds, will give nonsense. Recheck both fields and recalculate.

The result does not match what the doctor said

Clinics may measure you with different scales, wearing different clothes, or at a different time of day. Small differences in height or weight can shift BMI by a point or so. A difference of a decimal or two is normal.

I am not sure of my exact height

Measure again against a wall rather than estimating. If you cannot, use the most recent measurement you trust. People also lose a little height as they get older, so an old measurement may no longer be accurate.

The calculator will not accept my input

Make sure you are using numbers only, with a decimal point instead of a comma, and that no field is empty. Do not type unit names such as "kg" or "cm" into the number boxes.

My BMI says overweight but I feel fit

This is common for people who exercise a lot or have a muscular build. BMI does not know how much of your weight is muscle. Use it as one piece of information, not the final word.

Using the BMI Calculator on a Phone

Most people in Nigeria browse on Android phones, and this calculator works in the phone browser without installing anything. A few tips:

• Rotate your phone to landscape if the fields feel cramped.
• Use the phone's number keypad, and enter decimals with the dot key.
• If you have a Bluetooth or smart scale app that records your weight, check which unit it uses before copying the figure over.
• Convert units first if needed. Many phone calculators and search engines can convert feet to centimetres or pounds to kilograms in seconds.

Once you have your height and weight written down, the calculation takes only a few seconds even on a slow connection.

Using the BMI Calculator on a Computer

On a laptop or desktop, the process is the same, and it is slightly easier to type precise values. Some helpful points:

• Use the Tab key to move between the height and weight fields quickly.
• If you are comparing different scenarios, such as what your BMI would be at a target weight, you can change just the weight field and recalculate without re-entering your height.
• If you want to keep a record, note the date, weight and BMI in a spreadsheet or notebook so you can track change over time.

Privacy and Security

A BMI calculation involves personal health-related information, so it is reasonable to think about privacy before entering it. A few sensible habits apply to any online tool:

• Only enter height and weight. A BMI calculator does not need your name, phone number, address or any identification.
• If a calculator ever asks for personal details that have nothing to do with the calculation, do not provide them.
• Avoid using public or shared computers for anything you would rather keep private, or clear your browsing history afterwards.
• Remember that screenshots of your result can be shared by accident if you send them in group chats.

Please review the website's privacy policy if you want to understand how any data entered on a page is handled.

Why Use an Online BMI Calculator?

You can do the calculation by hand, but an online tool has some practical advantages:

• It removes the risk of arithmetic mistakes, especially when squaring decimals.
• It handles different units, so you do not need to convert between pounds and kilograms yourself.
• It gives you the category instantly, so you do not need to remember the ranges.
• It works on any device with a browser.
• It is quick enough to use again whenever your weight changes.

None of this replaces a medical assessment. The calculator simply saves time and removes small errors from an easy but fiddly calculation.

What Is a Healthy Weight Range for Your Height?

Instead of asking only "what is my BMI," many people find it more useful to ask "what weight range would put me at a BMI between 18.5 and 24.9?" You can work this out with simple multiplication:

• Lower limit: 18.5 × height in metres × height in metres
• Upper limit: 24.9 × height in metres × height in metres

For someone who is 1.70 m tall, height squared is 2.89

• 18.5 ? 2.89 = about 53.5 kg
• 24.9 ? 2.89 = about 72 kg

So the healthy BMI range for that height spans roughly 53.5 to 72 kg. For someone who is 1.65 m tall, the range is about 50.4 to 67.8 kg.

This is useful for goal setting. If your current weight is above the range, you may not need to reach the bottom of it. Even a modest, steady reduction can matter for many people, and a doctor can advise what target makes sense for you.

Where BMI Falls Short

Because BMI is so simple, it has known limits. Keep these in mind when you read your result:

• Muscle and athletic builds. Muscle weighs more than fat for the same volume, so athletes and people who do heavy physical work may score high without carrying excess fat.
• Older adults. With age, people tend to lose muscle and gain fat even if their weight stays the same, so BMI can look reassuring when body composition has shifted. Very low BMI in older adults can also be a concern in itself.
• Different body shapes and ethnic backgrounds. Research has shown that health risks can appear at different BMI levels for different populations. Some health bodies suggest lower cut-offs for certain groups. Your doctor can tell you whether adjusted guidance applies to you.
• Where fat is stored. Fat carried around the waist is generally linked to higher health risk than fat carried elsewhere, and BMI cannot see that. Waist circumference adds this missing detail.
• Pregnancy. BMI is not a suitable measure during pregnancy. Weight gain in pregnancy is monitored by midwives and doctors using different guidance.
• Children and teenagers. For people under 20, BMI is interpreted against growth charts that account for age and sex, so the adult categories do not apply. A paediatrician or child health nurse should interpret results for children.
• Illness and fluid. Swelling, fluid retention and some medical conditions can change body weight without changing body fat.

What to Do With Your Result

If your BMI is in the healthy range, you do not need to do anything special beyond keeping up habits that support your general health, such as balanced meals, regular movement, enough sleep and routine check-ups.

If it is outside the healthy range, avoid panic and avoid extreme responses such as crash diets or skipping meals. A better approach is to speak with a doctor, nurse or registered dietitian who can look at your full picture, including blood pressure, blood sugar, family history and lifestyle. Changes that are gradual and realistic tend to be easier to maintain than dramatic ones.

If you are underweight and unsure why, or if your weight has changed noticeably without any effort on your part, it is worth getting checked. Unexplained weight change can have causes that are easy to treat when found early.

This guide is for general information only and is not medical advice.

Why Two People With the Same BMI Can Be in Very Different Health

Once you have your number, the natural next question is what it really says about you. The honest answer is that BMI describes a relationship between weight and height and nothing more. Two adults who are both 1.72 m tall and 75 kg will both get a BMI of about 25.4, yet one may have a flat stomach, strong legs and good stamina, while the other carries most of his weight around the waist and rarely exercises. The formula sees them as identical. This is why doctors treat BMI as the first step in a conversation and not the end of it, and why it helps to build a fuller picture with a few other measurements.

Measurements That Add Context to BMI

Waist circumference

Of all the add-ons, waist measurement is the easiest to do at home and the most informative. Fat stored around the abdomen is linked to a higher risk of conditions such as type 2 diabetes and heart disease than fat stored on the hips or thighs. To measure, stand relaxed, breathe out normally, and wrap a soft tape around your middle at the level of your navel, keeping it snug but not pressing into the skin. Many health organisations publish waist guidelines, and these differ for men and women and sometimes for different ethnic groups, so it is worth asking a nurse or doctor which figure applies to you instead of relying on a number copied from a random website.

Waist-to-height ratio

A related idea is to divide your waist measurement by your height, using the same unit for both. Some researchers prefer this ratio because it adjusts for body size and is simple to understand. A commonly mentioned rule of thumb is that your waist should be less than half your height, though you should treat this as a rough guide and not a medical threshold. If you are 170 cm tall, for example, half your height is 85 cm, so a waist well above that would be a reason to look more closely at your lifestyle and speak with a health professional.

Blood pressure, blood sugar and cholesterol

These are the measurements that tell you what is happening inside the body, and they matter far more than any single weight figure. Someone with a BMI in the overweight range and perfectly normal blood tests is in a different position from someone with a healthy BMI and high blood sugar. In Nigeria, blood pressure and blood glucose checks are available at most pharmacies and primary health centres, often at low cost, and they are a practical way to find out whether your weight is affecting your health. Cholesterol testing usually needs a laboratory or clinic visit.

Body fat percentage

Some gyms, clinics and home scales estimate body fat percentage. These readings can be useful for watching your own progress, but the cheaper devices are not very accurate. Scales that send a tiny electrical current through your feet are easily thrown off by how much water you have drunk, whether you have just exercised, and even the time of day. If you use one, look at the trend over weeks and ignore day-to-day jumps.

How Often Should You Check Your BMI?

There is no value in calculating your BMI every day. Body weight naturally moves up and down with meals, hydration, salt intake, hormones and sleep, so a daily check mostly measures noise. A sensible rhythm for most people is once a month, or once every few months if you are not actively trying to change your weight. If you are following a plan to lose or gain weight, weighing yourself once a week at the same time and on the same scale, then recalculating BMI monthly, gives you a clearer view of the direction you are heading without turning the process into an obsession.

It is also worth saying that BMI does not need to be the goal. Many people do better focusing on habits such as walking more, eating regular balanced meals, drinking enough water and sleeping properly, and letting the number follow. If checking BMI regularly makes you anxious, or if you notice yourself becoming preoccupied with food or weight, that is a good reason to step back and talk to someone you trust or a health professional.

Realistic Ways to Move Toward a Healthier Range

If your BMI is above the healthy range

Sudden, extreme methods rarely last and can cause harm. A slower approach tends to work better. Start by looking at what you drink, since sweetened drinks, malt drinks and fruit juices can add a surprising number of calories without making you feel full. Pay attention to portion sizes of rice, yam, bread, garri, pasta and other starchy staples, which are healthy foods in sensible amounts but easy to overeat. Add vegetables, beans, eggs, fish or other protein to meals so you stay satisfied for longer. For movement, brisk walking is a good starting point for people who are not used to exercise, and it needs no equipment or membership. Even small changes, kept up for months, count for more than a strict programme abandoned after two weeks.

If you have a long-term condition such as high blood pressure, diabetes or a heart problem, or if you take regular medication, speak to your doctor before making large changes to your diet or exercise.

If your BMI is below the healthy range

Being underweight is not simply the opposite of being overweight, and it deserves the same care. First, it helps to find out whether there is a reason. Poor appetite, persistent stress, infections, digestive problems, thyroid conditions and other illnesses can all play a part, and so can simply not eating often enough. A doctor can check for these. If no medical cause is found, gradual gains usually come from eating more regularly, adding energy-dense and nutritious foods such as groundnuts, avocado, milk, eggs, beans and oils to meals, and including some strength-building activity so that the extra weight is more likely to be muscle than only fat. Supplements and weight-gain products sold without proper guidance are a poor shortcut, and some are unsafe.

BMI for Special Groups

Teenagers and children

The adult table does not apply to anyone below about 20. Young people are still growing, and what counts as a healthy BMI changes with age and differs between boys and girls. Health professionals plot a child's BMI on a growth chart and look at where it falls compared with other children of the same age and sex, using a measure called a percentile. If you are a parent worried about a child's weight, the most helpful step is to ask a doctor or child health nurse to assess the child properly. Putting a child on a diet based on an adult calculator result can do real harm.

Older adults

After about 65, the picture changes. Slightly higher weights are not always harmful in later life, while unintentional weight loss is often more concerning, because it can signal illness or loss of muscle. Older adults also lose height over time, which pushes BMI upward even if weight stays stable. For this group, a clinician will usually look at muscle strength, appetite, mobility and general function as well as BMI.

Pregnant and breastfeeding women

During pregnancy, BMI is not used to judge whether you are healthy, because your weight is expected to rise. Midwives and doctors normally use your weight before pregnancy to give guidance on how much gain is suitable for you, and they track it throughout antenatal visits. After delivery, weight changes gradually and differently for every woman, and there is no need to rush to a particular number. If you are breastfeeding, extreme dieting is discouraged because your body needs enough energy and nutrients, so ask your midwife or doctor for advice before changing what you eat.

Athletes and people who lift weights

People with a lot of muscle mass often land in the overweight category despite having low body fat. If you train seriously, waist circumference, body fat estimates from a trained professional and your performance and recovery will tell you more than BMI does. That does not mean BMI is useless for everyone who exercises, however. Many people who do regular exercise, such as walking, football or gym classes, do not have unusually high muscle mass, and for them BMI still works reasonably as a rough guide.

When BMI Is Not the Right Tool

There are situations where BMI should be set aside or used only with a professional's guidance. These include pregnancy, severe illness, conditions that cause fluid retention or swelling, recent surgery that has changed body weight, amputation, and eating disorders. If you have a history of an eating disorder, repeatedly calculating BMI can be unhelpful or even harmful, and a healthcare professional can suggest safer ways to monitor your wellbeing. Similarly, if you have been told by a doctor that your weight target is different from the standard range, follow that advice, because it was made with your full medical history in mind.

Practical Uses Beyond Personal Health

BMI shows up in more places than most people expect. Some insurers, fitness programmes, military and security recruitment processes, and certain medical procedures ask for it, though the cut-offs and rules vary and change, so you should confirm the current requirement directly with the organisation involved instead of relying on a fixed number from the internet. Students in nutrition, nursing, biology and public health courses often calculate BMI as a classroom exercise, and the worked examples in this guide can help you check your method. Writers and researchers dealing with health topics, whether in articles, reports or even fiction, can use BMI to describe a character's or a population's weight status in a way readers recognise, although it is wise to avoid presenting it as a judgment of someone's worth or health.

Common Mistakes to Avoid

The most common error is mixing units, for example typing height in centimetres into a box that expects metres. A second is comparing results from different days when your weight was measured under different conditions, such as after a heavy meal one day and fasting the next. A third is treating a category label as an identity, believing that "overweight" or "underweight" defines you, when it is simply a rough statistical grouping. Finally, many people use a single result to make a drastic decision, such as starting an extreme diet or stopping physical activity, when the better response is to gather more information and speak with someone qualified.

Related Tools and Next Steps

If you are tracking other numbers, such as percentages of weight lost or the difference between two readings, a percentage calculator can help you see change over time more clearly. For students using BMI in assignments, a general calculator can help you check the squaring and division by hand. Beyond calculators, the most valuable next step for anyone worried about their result is a simple visit to a clinic or pharmacy for blood pressure and blood sugar checks and a conversation about your habits and family history.

This guide is for general information only and is not a substitute for advice from a doctor, nurse or registered dietitian.

BMI Calculator FAQ

What is a normal BMI for an adult?

A BMI between 18.5 and 24.9 is generally treated as the healthy weight range for adults. Below 18.5 is classed as underweight, 25 to 29.9 as overweight, and 30 or above as obesity. These ranges come from World Health Organization guidance and are used for screening, so they are a starting point and not a diagnosis. Your doctor may interpret the number differently depending on your age, build, ethnic background and medical history.

How do I calculate my BMI?

Divide your weight in kilograms by your height in metres multiplied by itself. For example, someone who weighs 68 kg and is 1.70 m tall has a height squared of 2.89, so the BMI is 68 divided by 2.89, which is about 23.5. If you use pounds and inches, multiply your weight in pounds by 703, then divide by your height in inches multiplied by itself. The calculator above does all of this for you.

What is the BMI formula in pounds and inches?

The formula is weight in pounds multiplied by 703, divided by height in inches squared. A person who is 5 feet 6 inches (66 inches) and weighs 150 pounds would calculate 150 times 703, which is 105,450, then divide by 4,356 (66 times 66). The result is about 24.2. Remember to convert feet into inches first, since 5 feet 6 inches is 66 inches in total.

Is BMI accurate?

BMI is accurate as a measurement of weight relative to height, but it is not always accurate as a measure of health. It cannot tell muscle from fat, and it does not show where fat is stored. It works reasonably well as a quick screening tool across large groups of people. For one individual, it is best combined with waist measurement, blood pressure, blood sugar results and advice from a health professional.

Why is my BMI high even though I am not fat?

This usually happens when a large share of your weight is muscle, bone or water. Muscle is denser than fat, so people who lift weights, play sports or do physical labour can score in the overweight range without carrying much body fat. If this describes you, a waist measurement or a body composition check will say more than the BMI category does.

Can BMI be wrong?

Yes, BMI can be misleading in several situations. It may overestimate risk in very muscular people and underestimate it in older adults who have lost muscle and gained fat. It can also be thrown off by fluid retention, pregnancy and certain illnesses. It is a useful first look, but it should never be the only thing used to judge someone's health.

What BMI is considered underweight?

A BMI below 18.5 is classed as underweight for adults. This can be caused by not eating enough, long-term illness, stress, digestive problems, thyroid issues or simply a naturally slim frame. If your BMI is low and you have lost weight without trying, feel weak or tired, or notice other changes in your body, it is sensible to see a doctor to rule out a medical cause.

What BMI is considered overweight or obese?

A BMI from 25 to 29.9 is classed as overweight, and 30 or above falls in the obesity range, which is further divided into classes 1, 2 and 3. These labels describe a statistical grouping and do not describe a person's character or worth. A higher BMI can be linked with greater risk of some conditions, so it is worth discussing with a doctor, but it does not mean you are unwell.

What is the ideal weight for my height?

There is no single ideal weight, but there is a range. You can find the weight range that matches a BMI of 18.5 to 24.9 by multiplying those two numbers by your height in metres squared. For a person who is 1.65 m tall, that works out to roughly 50 to 68 kg. Where you should aim within or around that range depends on your age, muscle mass, medical conditions and personal goals.

Does BMI work for men and women?

The standard BMI formula and adult categories are the same for both men and women. However, women generally carry more body fat than men at the same BMI, so the same number can mean slightly different things for each. This is another reason it works better as a screening tool than a precise personal measurement.

Is BMI different for Africans or Black people?

Research suggests that the relationship between BMI and health risk can vary between ethnic groups, because body shape, muscle mass and fat distribution differ. Some health bodies recommend adjusted cut-offs for certain populations, mostly in studies of people of Asian descent. For people of African descent, the evidence is less settled and varies between studies. A doctor who knows your history can tell you how best to interpret your result.

Can I use the BMI calculator for a child or teenager?

No, the adult calculator and categories are not suitable for children and teenagers. Young people are still growing, and a healthy BMI changes with age and differs between boys and girls. Health professionals compare a child's BMI against growth charts that show percentiles for their age and sex. If you are concerned about a child's weight, ask a doctor or child health nurse to assess them.

Is BMI accurate for older adults?

BMI is less reliable in older adults. With age, people usually lose muscle, lose some height and tend to gain fat, so BMI can look normal even when body composition has shifted. Unintentional weight loss is also a bigger concern in later life than a slightly higher BMI. Doctors usually consider strength, appetite, mobility and general health along with the number.

Can I use a BMI calculator during pregnancy?

BMI is not a suitable way to judge health during pregnancy, because weight is expected to increase. Midwives and doctors normally use your pre-pregnancy weight and BMI to advise on how much gain is appropriate and monitor it at antenatal visits. If you are worried about your weight while pregnant, raise it at your next appointment instead of using a standard calculator.

How often should I check my BMI?

Checking once a month, or every few months if you are not trying to change your weight, is enough for most people. Daily weight varies because of food, water, salt, hormones and sleep, so frequent checks mostly record normal fluctuations. If you are working toward a goal, weighing weekly under the same conditions and calculating BMI monthly gives a clearer trend.

How can I lower my BMI safely?

The safest approach is gradual change that you can keep up. Reduce sweetened drinks, watch portions of starchy foods, add vegetables, beans, fish or eggs to meals, and build more walking or other activity into your week. Crash diets, unregulated slimming teas and skipped meals often backfire and can be harmful. If you have a medical condition or take medication, speak with your doctor before making large changes.

How can I increase my BMI if I am underweight?

Start by finding out whether there is a medical reason for low weight. If there is none, eat more regularly and add nutritious, energy-rich foods such as groundnuts, milk, eggs, beans, avocado and healthy oils. Some strength-building activity helps ensure the weight you gain includes muscle. Be careful with weight-gain supplements sold without proper guidance, because some are not safe.

Is BMI or waist circumference a better measure?

Neither is better in every case, and they answer different questions. BMI shows weight relative to height, while waist circumference shows how much fat is carried around the abdomen, which is linked to higher health risk. Using both gives a fuller picture than either alone. Many clinicians check both, together with blood pressure and blood sugar.

Why is my BMI different on different calculators?

Small differences usually come from rounding, different units or slightly different inputs. One calculator may round height to the nearest centimetre while another uses decimals, and since height is squared, small differences grow. A large gap usually means a unit was entered incorrectly, such as pounds instead of kilograms. Recheck your inputs and try again.

Can I use the BMI calculator on my phone?

Yes, the calculator works in the browser on Android phones, iPhones and computers without installing an app. Open the page, enter your height and weight using the units provided, and press calculate. If you have a slow connection, the page should still work once it has loaded, since the calculation itself is simple.

Is it safe to enter my height and weight into an online calculator?

A BMI calculator only needs height and weight, which are not enough to identify you. Be cautious if any calculator asks for your name, phone number, email or address, because these are not needed for the calculation. Avoid public computers for private health checks, and check the website's privacy policy if you want to know how entered data is handled.

Does BMI tell me if I am healthy?

No, BMI alone cannot tell you whether you are healthy. It is a quick indicator of weight relative to height and nothing more. Real health depends on things like blood pressure, blood sugar, cholesterol, fitness, diet, sleep, mental wellbeing and family history. A normal BMI does not guarantee good health, and a high or low one does not guarantee poor health.

When should I see a doctor about my BMI?

Speak with a doctor if your BMI is well outside the healthy range, if your weight has changed noticeably without effort, or if you have symptoms such as constant tiredness, breathlessness, swelling or loss of appetite. It is also worth a visit if you have a family history of diabetes, high blood pressure or heart disease and want advice on prevention.

Before You Go

Your BMI is a single number, and it is most useful when you treat it as a prompt for the next question instead of a final answer. If it falls in the healthy range, keep doing what supports your general wellbeing. If it does not, take the next small step: measure your waist, check your blood pressure at a pharmacy, and talk to a doctor or dietitian about what makes sense for you. You can come back to the calculator above whenever your weight changes, and you can use the examples and measurements in this guide to understand what the result means for you.

This guide is for general information only and is not a substitute for advice from a doctor, nurse or registered dietitian.