BMI Calculator: Your Body Mass Index and Healthy Range
Enter your height and weight and get your body mass index, the WHO category it falls in, and the healthy weight range for your height in both kilos and pounds. Nothing is stored and nothing is sent anywhere.
Your body mass index is
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kg/m²
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How we got your number
BMI is weight in kilograms divided by height in metres squared. Pounds and feet are converted first, at 1 lb = 0.453592 kg and 1 in = 2.54 cm. Categories follow the WHO classification for adults.
Healthy weight for your height
The same band in pounds is shown alongside. A range this wide is normal: BMI says nothing about what the weight is made of.
The WHO categories in full
| Category | BMI | Weight at your height |
|---|
Your own band is highlighted. Weights are worked back from the cutoffs using your height.
Lower thresholds for Asian populations
A WHO expert consultation in 2004 looked at the evidence that risk of type 2 diabetes and cardiovascular disease starts climbing at a lower BMI in many Asian populations than in European ones, at the same index value. Rather than redraw the categories, it proposed additional public health action points at 23 for increased risk and 27.5 for high risk.
Those figures are used in national guidance in countries including Singapore, China, Japan and India, and by several clinicians elsewhere for patients of South Asian, Chinese and South East Asian descent. The relevant population here is ancestry, not the country you live in.
Where BMI gets it wrong
Muscle. Muscle is denser than fat, so a trained body weighs more at the same size. Rowers, sprinters, rugby forwards and most committed lifters read overweight or obese with very low body fat. The number is not measuring what you think it is measuring.
Pregnancy. BMI is not interpreted during pregnancy. Weight gain is expected and planned, and the figure that matters to a midwife is your pre-pregnancy BMI, which sets the recommended gain for the nine months.
Older adults. People lose muscle and bone with age while keeping or gaining fat, so BMI can stay flat while body composition worsens. In over-65s a slightly higher BMI is associated with better outcomes, and some guidance moves the healthy band up to roughly 23 to 27.
Children and teenagers. The adult cutoffs do not apply at all. A growing body changes shape with age and sex, so paediatric BMI has to be read against percentile curves from the CDC or the WHO growth standards, where healthy sits between the 5th and 85th percentile for that exact age and sex. A single number cannot do that job.
The index is nearly two centuries old. Adolphe Quetelet, a Belgian astronomer and statistician, divided weight by height squared in 1832 while building a statistical portrait of l'homme moyen, the average man of a population. He was describing groups, not diagnosing individuals, and the ratio was never intended to be read off a chart in a consulting room. It only picked up the name body mass index in 1972, when Ancel Keys tested it against the other weight-for-height measures of the day and found it the best of a poor field for population work.
That history explains both why BMI survives and why it irritates people. It survives because it is almost free: two numbers anyone can measure, a formula that behaves the same in every clinic and every country, and decades of data linking the bands to rates of type 2 diabetes, heart disease and joint problems across large groups. Sorting a population into rough risk tiers is exactly the job it was built for, and nothing cheaper does that job better.
What it cannot do is tell you what you are made of. BMI measures weight against height, not fat against lean tissue, and it has no idea where the weight sits. A rower and a sedentary office worker of the same height and weight get the same number, and only one of them has a problem to solve. Distribution matters as much as total, which is why the NHS pairs the index with a tape measure: a waist over 94 cm in men or over 80 cm in women signals raised risk even when BMI reads normal, and over 102 cm or 88 cm respectively signals high risk.
So treat the number as a question rather than an answer. If it lands in the healthy band and your waist is under those thresholds, there is little here to act on. If it is high, your waist, your blood pressure and your blood sugar will tell you far more about what to do next than the index itself. And if you are adding muscle on purpose, expect BMI to rise, and judge the result by the tape rather than the chart.
More free calculators
Work out the rest of your numbers: the daily calorie calculator, the BMR calculator, the ideal weight calculator, the calories burned calculator and the recipe nutrition calculator. The full list is on the calculators page.
Frequently asked questions
What is a healthy BMI?
The World Health Organization puts the healthy range at 18.5 to 24.9 for adults. Below 18.5 is classed as underweight, 25 to 29.9 as overweight, and 30 and above as obese. The band is wide on purpose: at 1.70 m it covers everything from 53.5 kg to 72.0 kg, which is a spread of nearly nineteen kilos.
Is BMI accurate for muscular people?
No. Muscle is denser than fat, so a trained body weighs more for the same size and the index reads high. Rugby forwards, sprinters and most serious lifters land in the overweight or obese bands with single-digit body fat. If you carry visible muscle, use a waist measurement or a body fat estimate instead and treat BMI as background noise.
What BMI is considered obese?
A BMI of 30 or above. The WHO splits it further into class I from 30 to 34.9, class II from 35 to 39.9, and class III at 40 and above, which is sometimes called severe obesity. The classes matter clinically because risk rises steeply between them rather than smoothly.
Does BMI work for children?
Not in the adult form. Children and teenagers are still growing, and body composition changes with age and sex, so the same number means different things at 7 and at 15. Paediatric BMI is read against age and sex percentile curves from the CDC or the WHO growth standards, where the healthy band is the 5th to the 85th percentile. Use a chart made for children, or ask a doctor.
What should my weight be for my height?
Multiply your height in metres by itself, then multiply that by 18.5 for the bottom of the healthy range and by 24.9 for the top. At 1.75 m that gives 56.7 kg to 76.3 kg, or 125 lb to 168 lb. The calculator above does it for your height and tells you how far outside the range you are, if you are outside it at all.
Is BMI different for men and women?
The formula and the cutoffs are the same for both. Women carry more essential fat than men at any given BMI, which is one reason the index is a poor measure of body composition, but the WHO thresholds were set on mixed adult populations and are not split by sex. Age and sex are only used on this page for context, not in the sum.
Should Asian adults use lower BMI thresholds?
Often, yes. A WHO expert consultation in 2004 found that many Asian populations show raised diabetes and cardiovascular risk at a lower BMI than European populations, and proposed action points at 23 for overweight and 27.5 for obesity. Several countries, including Singapore, China, Japan and India, use thresholds in that region. It is a public health trigger point, not a separate diagnosis.
How this calculator works
Sources
- World Health Organization — obesity and overweight, BMI classification. www.who.int
- NHS — managing your weight. www.nhs.uk
This calculator is for general information and is not medical advice. It is not suitable if you are under 18, pregnant or breastfeeding, or being treated for an eating disorder or a condition that affects weight. Speak to your GP or a registered dietitian before acting on the numbers.