Is BMI accurate for muscular people?

No. BMI is a ratio of mass to height and contains no information about body composition, so muscle and fat count identically. A trained athlete can read in the overweight or obese range while carrying very little body fat. If body composition is the question, the body fat calculator answers it more directly.

What is a healthy BMI?

The WHO healthy band runs from 18.5 up to but not including 25. The widely repeated "18.5 to 24.9" is a rounding of the same thing: the real boundary is 25.0, so a BMI of 24.95 is inside the band.

Does BMI work the same for everyone?

The cut-points were derived largely from European-descent populations. The WHO itself notes that the relationship between BMI and health risk differs across populations, and several countries use lower thresholds for people of South and East Asian descent. Treat the categories as a rough screening step rather than a fixed rule.

Should children use this?

No. Adult BMI categories do not apply to anyone under 18, because body composition changes substantially with growth stage. Paediatric assessment uses age and sex-specific percentile charts instead, which a doctor can interpret properly.

What is the difference between BMI and BMI Prime?

None mathematically — BMI Prime is BMI divided by 25. Its only advantage is readability: 1.10 immediately says "10% above the upper healthy bound", where a BMI of 27.5 requires you to remember where the boundary sits.

Why does BMI over-read for tall people?

Because it divides by height squared, while human bodies scale closer to height cubed in some dimensions and less than squared in others. The exponent of 2 was chosen because it fit the population data of the time, not because it describes an individual body. The ponderal index uses a cube and behaves better at the extremes.

BMI calculator

Enter your height and weight to get your body mass index, the WHO category it falls in, and the weight range that corresponds to a healthy BMI at your height.

Result

These are estimates from population-level equations, not a measurement of you and not medical advice. Individual results vary widely. Talk to a doctor or a registered dietitian before making significant changes to how you eat or train.

How this is calculated

Body mass indexdefault

              BMI = mass (kg) / height (m)²

Source: Quetelet A., 1835. Named "body mass index" by Keys A. et al., Journal of Chronic Diseases 25(6), 1972, pp. 329–343. Category cut-points: WHO Technical Report Series 894, 2000.
Assumes: That mass scales with the square of height across the population. It carries no information about what the mass is made of.
Accuracy: Reliable as a population screening indicator. For an individual it cannot distinguish muscle from fat, and it systematically over-reads for tall people and under-reads for short ones, because human bodies do not scale exactly with the square of height.

BMI Prime

              BMI Prime = BMI / 25

Source: Gadzik J., "How much should I weigh?", Connecticut Medicine 70(2), 2006, pp. 81–88.
Assumes: The same as BMI, expressed relative to the upper healthy bound.
Accuracy: Adds no new information — it is BMI rescaled — but makes distance from the band edge readable without memorising cut-points. A value of 1.0 sits exactly at BMI 25.

Ponderal index

              PI = mass (kg) / height (m)³

Source: Rohrer F., Münchener Medizinische Wochenschrift 68, 1921.
Assumes: That mass scales with the cube of height rather than the square.
Accuracy: More stable than BMI at the extremes of height, which is exactly where BMI is weakest. Less useful in the middle of the range, where BMI has far more published reference data behind it.

Which formula should you use

This page defaults to Body mass index. Reliable as a population screening indicator. For an individual it cannot distinguish muscle from fat, and it systematically over-reads for tall people and under-reads for short ones, because human bodies do not scale exactly with the square of height.

BMI Prime — Adds no new information — it is BMI rescaled — but makes distance from the band edge readable without memorising cut-points. A value of 1.0 sits exactly at BMI 25.
Ponderal index — More stable than BMI at the extremes of height, which is exactly where BMI is weakest. Less useful in the middle of the range, where BMI has far more published reference data behind it.

BMI by height and weight

Read across from your height and down from your weight. Values of 18.5 to 25 fall in the WHO healthy band. BMI cannot tell muscle from fat, so a very muscular person can read high without carrying excess fat.

BMI by height and weight
Height	50 kg	60 kg	70 kg	80 kg	90 kg	100 kg	110 kg
155 cm	20.8	25	29.1	33.3	37.5	41.6	45.8
160 cm	19.5	23.4	27.3	31.2	35.2	39.1	43
165 cm	18.4	22	25.7	29.4	33.1	36.7	40.4
170 cm	17.3	20.8	24.2	27.7	31.1	34.6	38.1
175 cm	16.3	19.6	22.9	26.1	29.4	32.7	35.9
180 cm	15.4	18.5	21.6	24.7	27.8	30.9	34
185 cm	14.6	17.5	20.5	23.4	26.3	29.2	32.1
190 cm	13.9	16.6	19.4	22.2	24.9	27.7	30.5

Questions

Is BMI accurate for muscular people?: No. BMI is a ratio of mass to height and contains no information about body composition, so muscle and fat count identically. A trained athlete can read in the overweight or obese range while carrying very little body fat. If body composition is the question, the body fat calculator answers it more directly.
What is a healthy BMI?: The WHO healthy band runs from 18.5 up to but not including 25. The widely repeated "18.5 to 24.9" is a rounding of the same thing: the real boundary is 25.0, so a BMI of 24.95 is inside the band.
Does BMI work the same for everyone?: The cut-points were derived largely from European-descent populations. The WHO itself notes that the relationship between BMI and health risk differs across populations, and several countries use lower thresholds for people of South and East Asian descent. Treat the categories as a rough screening step rather than a fixed rule.
Should children use this?: No. Adult BMI categories do not apply to anyone under 18, because body composition changes substantially with growth stage. Paediatric assessment uses age and sex-specific percentile charts instead, which a doctor can interpret properly.
What is the difference between BMI and BMI Prime?: None mathematically — BMI Prime is BMI divided by 25. Its only advantage is readability: 1.10 immediately says "10% above the upper healthy bound", where a BMI of 27.5 requires you to remember where the boundary sits.
Why does BMI over-read for tall people?: Because it divides by height squared, while human bodies scale closer to height cubed in some dimensions and less than squared in others. The exponent of 2 was chosen because it fit the population data of the time, not because it describes an individual body. The ponderal index uses a cube and behaves better at the extremes.

Calculators

Guides

Last reviewed August 20, 2026. Category: Body composition.