BMI Calculator
Calculate Body Mass Index in metric or imperial units with the WHO category scale.
Body Mass Index Calculator with the WHO Category Scale
Body Mass Index divides weight by the square of height to give a single number that is easy to compare across a population. It was designed in the nineteenth century as a statistical tool for describing groups, and it remains the standard first-pass screening measure used by health services worldwide.
This calculator accepts metric or imperial input and shows where the result sits on the World Health Organization scale. Because everything runs in your browser, your height and weight — genuinely sensitive information — never leave your device.
Key features
- Both unit systems — kilograms and centimetres, or pounds with feet and inches.
- WHO category scale — underweight, healthy, overweight and obese thresholds shown in full.
- Visual position — a meter shows where your reading falls, colour-coded by band.
- Complete privacy — height and weight are processed locally and never transmitted.
This tool runs entirely inside your browser using native Web APIs. Your files and text are never uploaded to a server, never logged and never shared with third parties.
How to use: BMI Calculator
- Choose your unit system
Switch between metric (kg / cm) and imperial (lb / ft + in) at the top. - Enter height and weight
The BMI figure and its category update as you type. - Read the category
The colour and label place your reading against the WHO thresholds listed in the table below. - Interpret it in context
BMI is a screening indicator, not a diagnosis. Build, muscle mass, age and ethnicity all affect what a given number means for an individual.
Technical specifications
| Processing location | Entirely in your browser — no server round trip |
|---|---|
| Data uploaded | None. Files and text never leave your device |
| Price | Free — no account, no trial, no usage cap |
| Category | Calculators |
| Works offline | Yes, once the page has loaded |
| Browser support | Chrome 90+, Edge 90+, Firefox 90+, Safari 15+ |
| Interface languages | English, 中文, हिन्दी, Español, العربية |
Frequently asked questions
What is a healthy BMI range?
The World Health Organization defines 18.5 to 24.9 as the healthy range for adults, with below 18.5 underweight, 25 to 29.9 overweight and 30 or above obese. Some health bodies use lower thresholds for people of South Asian descent, where cardiometabolic risk rises at a lower BMI.
Is BMI accurate for athletes?
Often not. BMI cannot distinguish muscle from fat, and muscle is denser. A lean, heavily built athlete can register as overweight or obese while carrying very little body fat. Body composition measurement is more appropriate in that case.
Does BMI work for children?
Not in the same way. Children and teenagers are assessed against age- and sex-specific percentile charts rather than the fixed adult thresholds, because body composition changes throughout growth.
How is BMI calculated?
Metric: weight in kilograms divided by height in metres squared. Imperial: weight in pounds divided by height in inches squared, multiplied by 703. The 703 factor simply converts the imperial result onto the metric scale.