How to Calculate BMI and What Your Result Actually Means
Calculate your BMI from height and weight in metric or imperial units, understand the weight categories, and learn what the number does not tell you.
BMI is the quickest way to see whether your weight sits in a healthy range for your height, and it takes two numbers and one formula. It is also widely misunderstood, so it helps to know both how to calculate it and what it does not tell you.
What BMI is
Body mass index (BMI) is a single number that relates your weight to your height. It is used as a quick screening tool to flag whether someone may be underweight, at a healthy weight, overweight, or obese. It does not measure body fat directly; it estimates risk at a population level.
The BMI formula
Metric: BMI = weight (kg) ÷ height (m)²
Imperial: BMI = 703 × weight (lb) ÷ height (in)²
For example, someone 1.75 m tall weighing 70 kg has a BMI of 70 ÷ (1.75 × 1.75) = 70 ÷ 3.06 = 22.9.
What the categories mean
- Under 18.5: underweight
- 18.5 to 24.9: healthy weight
- 25.0 to 29.9: overweight
- 30.0 and above: obese
These ranges apply to most adults. They are read differently for children, pregnant people, and athletes.
Where BMI falls short
BMI cannot tell muscle from fat, so a muscular athlete can register as "overweight" while carrying very little fat. It also ignores where fat is stored, which matters for health, and its accuracy varies across ages and ethnic groups. Treat it as a starting point, not a diagnosis, and pair it with measures like waist circumference and a doctor's input.
Calculate yours
The BMI calculator works in metric or imperial units and shows your category instantly. It runs entirely in your browser, so your height and weight are never uploaded.