Is BMI accurate for athletes?

Often not. Muscle is denser than fat, so a heavily trained athlete can score in the overweight or obese range while carrying very little body fat. Body-fat percentage and waist circumference are better measures in that case.

Can I use this BMI calculator for children?

No. Children and teenagers are assessed against age- and sex-specific percentile charts, because healthy body composition changes throughout growth. Ask a paediatrician or use a dedicated child growth chart.

What waist measurement matters alongside BMI?

Health authorities commonly flag increased risk above roughly 94 cm (37 in) for men and 80 cm (31.5 in) for women, because abdominal fat is more strongly linked to metabolic risk than total weight.

BMI Calculator

Body Mass Index compares your weight to your height and places the result in one of the World Health Organization's weight categories. It is a screening number, not a diagnosis — it says nothing about how much of your body mass is muscle.

Fill in the fields above and select Calculate to see your result and the full working.

Please note: Health calculators on this site provide general estimates based on population-level formulas. They are not medical advice and cannot account for your individual medical history. Speak to a qualified healthcare professional before making decisions about diet, medication or training.

Formula used

BMI = weight (kg) ÷ height (m)²

In imperial units the same relationship is written BMI = 703 × weight (lb) ÷ height (in)².

How to use this calculator

Choose metric or imperial units.
Enter your height — centimetres if you picked metric, inches if you picked imperial.
Enter your current weight in kilograms or pounds to match.
Press Calculate to see your BMI, its category and the healthy weight range for your height.

Example calculation

Someone 175 cm tall weighing 70 kg:

Height in metres = 175 ÷ 100 = 1.75 m

1.75² = 3.0625

BMI = 70 ÷ 3.0625 = 22.9 — inside the healthy-weight band.

What does this result mean?

The WHO bands are: under 18.5 underweight, 18.5–24.9 healthy weight, 25–29.9 overweight, and 30 or above obesity. BMI works reasonably well across large populations but poorly for individuals with a lot of muscle, for pregnant people, for the very short or tall, and for children, who need age-and-sex percentile charts instead. Treat a result near a boundary as a prompt to look at waist measurement, blood pressure and activity levels rather than a verdict.

Frequently asked questions

Is BMI accurate for athletes?: Often not. Muscle is denser than fat, so a heavily trained athlete can score in the overweight or obese range while carrying very little body fat. Body-fat percentage and waist circumference are better measures in that case.
Can I use this BMI calculator for children?: No. Children and teenagers are assessed against age- and sex-specific percentile charts, because healthy body composition changes throughout growth. Ask a paediatrician or use a dedicated child growth chart.
What waist measurement matters alongside BMI?: Health authorities commonly flag increased risk above roughly 94 cm (37 in) for men and 80 cm (31.5 in) for women, because abdominal fat is more strongly linked to metabolic risk than total weight.

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