Tools.ly
العربية
Health & fitness Works offline

BMI Calculator

Enter your height and weight to get your body mass index, the WHO category it falls into, and the weight range that would put you in the healthy band.

By Tools.ly Team Published

Estimates for information only. BMI cannot distinguish muscle from fat and is not valid in pregnancy or for children. It is not medical advice.

Units
Body mass index uses the WHO category boundaries. The healthy weight range is the weight at which your height gives a BMI between 18.5 and 24.9.

What BMI is, and what it is not

Body mass index is a single division: your weight in kilograms divided by the square of your height in metres. It was devised in the nineteenth century by Adolphe Quetelet as a way of describing populations, and it is still used that way today — to compare groups, track trends and triage large numbers of people cheaply. It was never designed to describe an individual body, and that is the source of most of the frustration it causes.

What it captures is weight relative to height. What it cannot capture is composition. A kilogram of muscle and a kilogram of fat weigh the same, so a rugby forward with 12 % body fat and a sedentary person with 32 % body fat can share the same BMI. The tool above therefore reports the number and the range, and then stops short of telling you what to do about it.

Reading the bands

The World Health Organization defines underweight as below 18.5, a healthy weight as 18.5 to 24.9, overweight as 25 to 29.9, and obesity in three classes from 30 upward. Those numbers come from population studies of risk, not from any property of an individual. They describe where average risk begins to rise, which is why they are used as action points rather than as targets.

The healthy weight range shown above is the honest translation of the healthy band for your height: the weights at which your BMI would sit between 18.5 and 24.9. Notice how wide it is — usually around fifteen to twenty kilograms at adult heights. Two people at the opposite ends of that range can both be healthy, and the space between them is where most of the disagreement about "ideal weight" lives.

Waist measurement matters more than you would think

Where fat sits is a stronger predictor of metabolic risk than how much of it there is. Fat stored around the abdominal organs — visceral fat — is associated with insulin resistance, type 2 diabetes and cardiovascular disease in a way that fat stored on the hips and thighs is not. That is why the tool accepts an optional waist measurement and flags it separately from the BMI result.

The usual action levels are 94 cm for men and 80 cm for women, with substantially increased risk at 102 cm and 88 cm respectively. Measure at the midpoint between the lowest rib and the top of the hip bone, at the end of a normal breath out, without pulling the tape tight. A waist that falls while your weight stays flat usually means fat is being replaced by muscle — a good outcome that a scale alone would hide.

Where BMI genuinely misleads

  • Trained muscle. Athletes and regular lifters are routinely misclassified as overweight.
  • Older adults. Muscle is lost with age, so a normal BMI can hide a high body-fat percentage.
  • South Asian and other Asian populations. Risk rises at a lower BMI; many guidelines use 23 rather than 25 as the first action point.
  • Pregnancy. The calculation has no meaning at all.
  • Children and teenagers. They need age- and sex-specific percentile charts, not adult bands.
  • Amputations and fluid retention. Both change the relationship between weight and body size drastically.

Weight is one measurement among many. Blood pressure, blood glucose, waist circumference, sleep, strength and how you actually feel tell a fuller story than any single number on this page. If you are considering a significant change to how you eat or train, talk to a doctor or registered dietitian first.

Frequently asked questions

Is BMI a good measure of my health?

It is a useful screening number and a poor individual diagnosis. Body mass index was designed to compare populations, and it only relates weight to height — it cannot tell muscle from fat, it says nothing about where fat sits, and it ignores fitness, blood pressure, blood glucose and family history. Use it as one input to a conversation with a clinician, not as a verdict on your body.

Why does my BMI say overweight when I am clearly fit?

Because muscle is denser than fat. A trained athlete can carry enough muscle to be classified as overweight or even obese while having a low body-fat percentage and excellent metabolic markers. In that case the waist measurement and how you perform matter far more than the BMI band.

Do the same thresholds apply to everyone?

No. Several health bodies use lower action points for people of South Asian, Chinese and other Asian populations, where the risk of type 2 diabetes and cardiovascular disease rises at a lower BMI — often 23 rather than 25. Some guidelines also adjust for age, since older adults tend to carry more fat at the same BMI.

When should I not use this at all?

During pregnancy, for children and teenagers (who need age- and sex-specific growth charts), for people with significant fluid retention or amputations, and for anyone whose clinician has told them that BMI is unreliable in their case. In those situations, ask a professional instead of reading a number off a web page.

Sources & further reading