BMI Calculator
BMI — body mass index — is the simplest health number in common use: your weight divided by your height squared. It takes ten seconds, needs no equipment beyond a scale and a tape measure, and it is genuinely useful as a first-pass signal. It is also, on its own, a terrible judge of any individual person. This page gives you the number, the category and the healthy range for your height — and then tells you honestly what it can and cannot say about you.
BMI is a screening number, not a diagnosis. It cannot tell muscle from fat — do not judge yourself by it.
How BMI is calculated
The formula is deliberately simple. In metric units:
BMI = weight (kg) ÷ height (m)²
For example, at 80 kg and 1.78 m: 80 ÷ (1.78 × 1.78) = 25.2. The World Health Organization’s adult categories are:
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese |
The “healthy weight for your height” figure in the result is simply the weight range that produces a BMI between 18.5 and 24.9 at your height.
What BMI gets right — and wrong
BMI is genuinely useful at population level and as a first-pass personal signal: if it is well outside the healthy band, that is worth paying attention to. But it has real limits, and you should know them before the number means anything to you:
- It cannot tell muscle from fat. A strength athlete at 95 kg can land in “overweight” with very little body fat.
- It says nothing about where fat sits. Waist size matters independently — a waist above roughly half your height deserves attention whatever your BMI says.
- It was built on adult averages. It does not apply to children (who use age-based percentiles), and it can mislead for older adults and across ethnic groups, where risk can rise at lower BMIs.
Our guide BMI: Useful Signal, Terrible Judge goes deeper, including the waist-to-height check you can do with a piece of string.
If your BMI is outside the healthy range
Treat it as a prompt, not a verdict. A sensible next step is a calorie target you can actually sustain and a re-check in a few months — and if the number worries you, a conversation with your doctor beats any website, this one included. BMI categories are screening bands, not diagnoses.