Health
BMI calculator (body mass index)
Enter weight and height: your BMI appears at once, with its class on a colour gauge and the weight considered healthy for your height.
What BMI measures
BMI, the body mass index, is weight in kilograms divided by the square of height in metres. At 72 kg and 1.75 m it is 72 / 1.75² ≈ 23.5. In pounds and inches the formula is 703 × weight / height². It is the quickest way to relate weight to height and is used worldwide for adults.
The World Health Organization defines underweight as a BMI below 18.5, healthy weight from 18.5 to 24.9, overweight from 25 to 29.9 and obesity from 30, split into three classes. The same thresholds applied to your height give the weight range considered healthy.
BMI is a statistical indicator, not a diagnosis: it cannot tell muscle from fat or say where fat is carried. For a fuller picture, pair it with waist circumference or body fat percentage.
Common mistakes
- Using height in centimetres without converting to metres: the result comes out 10,000 times too small.
- Applying adult classes to children and teenagers, who are assessed on growth charts by age.
- Reading a high BMI as excess fat in someone with a lot of muscle.
Frequently asked questions
What is a healthy BMI?
For adults the healthy range is 18.5 to 24.9. There is no single ideal value: within the range, age, build and lifestyle matter too.
Does BMI apply to older adults?
It is used after 65 as well, but some studies suggest a slightly higher BMI, up to about 27, carries no extra risk in later life.
Is BMI the same for men and women?
Yes, the formula and classes are the same. At the same BMI, though, women carry a higher fat percentage on average.
How this calculation works
BMI = weight (kg) / height (m)². In US units: 703 × weight (lb) / height (in)². The healthy weight range is 18.5 × height² to 24.9 × height², with height in metres.
Related calculators
Ideal weight
Ideal weight by the Devine, Robinson, Miller, Hamwi and Lorentz formulas, set against the healthy BMI range.
Calorie calculator
Basal metabolic rate and daily calories by the Mifflin–St Jeor equation, to maintain, lose or gain weight.
Body fat
Body fat percentage by the US Navy method from neck, waist and hips, with fat and lean mass.