BMI Calculator
BMI is weight in kilograms divided by height in metres squared. It is a screening number, not a diagnosis – a quick way for health services to flag who might benefit from a closer look. The calculator gives your figure and the WHO band it lands in; this page explains what that band actually means.
The formula, both ways
Metric: BMI = weight (kg) ÷ height (m)²
Imperial: BMI = 703 × weight (lb) ÷ height (in)²
So a person 1.75 m tall (about 5 ft 9 in, the US male average) weighing 78 kg has a BMI of 78 ÷ 1.75² = 25.5.
WHO categories
| BMI | Category |
|---|---|
| under 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and over | Obese |
Where BMI misleads
BMI does not know the difference between muscle and fat, so a lean, muscular athlete can read “overweight” with very low body fat. It also ignores where fat sits – visceral fat around the organs carries more risk than the same weight on the hips. It was derived from 19th-century European population data and fits some groups better than others. Treat it as one input among several, alongside waist measurement and how you actually feel. To estimate calorie needs from the same height and weight, use the BMR calculator.
FAQ
What is a healthy BMI?
The WHO puts the healthy range at 18.5 to 24.9 for most adults. Below 18.5 is underweight; 25 to 29.9 is overweight; 30 or more is obese.
Is BMI accurate for athletes?
Not very. Muscle is denser than fat, so a muscular person can have a high BMI with low body fat. Body-fat measurement is more useful for athletic builds.
Does BMI work for children?
The formula is the same, but the result is read against age- and sex-specific percentile charts, not the adult bands. A paediatrician should interpret a child's BMI.
How do I calculate BMI in pounds and inches?
BMI = 703 × weight (lb) ÷ height (in)². For 160 lb and 68 in: 703 × 160 ÷ 4624 = 24.3.
Is BMI the same as body fat percentage?
No. BMI is a height-to-weight ratio that estimates fatness indirectly. Body fat percentage measures fat mass directly and can differ a lot between two people with the same BMI.