BMI Calculator
Body mass index and what the number actually means.
About this tool
Body mass index is the World Health Organization's reference indicator for placing your weight against your height: weight in kilograms divided by height in metres squared. This calculator gives your BMI plus its interpretation against the official thresholds — underweight, healthy weight, overweight, obesity — and the healthy weight range for your height.
It works in metric (kg/cm) or imperial (lb/ft and inches), whichever you think in. The calculation stays in your browser: no health data is transmitted, stored or logged anywhere.
Frequently asked questions
What are the official BMI categories?
Per the WHO: under 18.5 is underweight; 18.5 to 24.9 is a healthy weight; 25 to 29.9 is overweight; 30 and above is obesity.
Is BMI reliable for everybody?
It is a population-level statistic, not a diagnosis. It cannot tell muscle from fat, so it reads high for athletes, and it should be interpreted differently for older adults, pregnant women and children. Talk to a healthcare professional before drawing conclusions.
What is the BMI formula?
BMI = weight (kg) ÷ height² (m). For example, 70 kg at 1.75 m gives 70 ÷ 3.0625 = 22.9. In imperial units it is weight (lb) × 703 ÷ height² (in).
What is a healthy weight for my height?
The calculator shows the range that corresponds to a BMI between 18.5 and 24.9 for the height you entered, in kilograms or pounds.
Is it really free, with no sign-up?
Yes — the tool is free, needs no account and has no usage limit. Processing happens locally in your browser, so your data never leaves your device.