BMI Calculator
The BMI Calculator works out your Body Mass Index from your height and weight and places you in the standard categories - underweight, normal, overweight, or obese - defined by the World Health Organization.
How BMI is calculated
Body Mass Index is your weight in kilograms divided by the square of your height in metres (kg/m²). For example, 70 kg at 1.75 m gives 70 ÷ (1.75 × 1.75) = 22.9. The WHO ranges are: below 18.5 underweight, 18.5–24.9 normal, 25–29.9 overweight, and 30 or above obese.
What BMI does and doesn't tell you
BMI is a quick, useful screening number for populations, but it does not measure body fat directly and does not distinguish muscle from fat. A muscular athlete can read as "overweight" while carrying little fat. Treat BMI as one signal among several, and see the Body Fat Calculator for a complementary view.
Frequently Asked Questions
What is a healthy BMI range?
For most adults a BMI between 18.5 and 24.9 is considered healthy. Below 18.5 is underweight and 25 or above is overweight.
Is BMI accurate for athletes?
Not always. BMI cannot tell muscle from fat, so very muscular people may score as overweight despite low body fat. Use it alongside other measures.
Does BMI work the same for men and women?
The standard adult BMI formula and ranges are the same for men and women. Body composition differs, which is one reason BMI is only a screening tool.
Is BMI suitable for children?
Children use age- and sex-specific BMI percentiles rather than the fixed adult ranges, so consult a paediatric chart or doctor for under-18s.
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