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BMI Calculator

Check your Body Mass Index in seconds. Our free BMI calculator takes your height and weight and instantly shows your BMI value plus your weight category — underweight, healthy, overweight, or obese — based on standard World Health Organization ranges.

  • Free, no signup
  • Runs in your browser
  • Works on mobile

How to use the BMI Calculator

  1. Choose metric (centimetres and kilograms) or imperial (feet, inches and pounds).
  2. Enter your height and weight. Switching units converts the numbers you have already typed.
  3. Your BMI, category and the healthy weight range for your height appear instantly.
  4. The marker on the colour scale shows where you sit between underweight and obese.

About this tool

BMI is your weight in kilograms divided by your height in metres squared. It is a quick screening measure used by doctors and the World Health Organization: under 18.5 is underweight, 18.5 to 24.9 healthy, 25 to 29.9 overweight and 30 or more obese. It is a general guide for adults, not a medical diagnosis, and it does not distinguish muscle from fat.

Why use itBMI is the quickest screening snapshot of weight-related health: doctors, insurers, and fitness programs all use it as a starting point. Knowing your number — and which category it falls into — helps you set realistic goals and track progress over time. Our calculator does the math instantly and color-codes your result, so your category is clear at a single glance.

Frequently asked questions

What is a healthy BMI?

Between 18.5 and 24.9 is considered the healthy range for most adults, according to the World Health Organization.

Is BMI accurate for athletes?

Not always — very muscular people can have a high BMI without excess body fat. BMI is a screening tool, not a diagnosis; athletes should also consider body-fat percentage and waist measurements.

Does age affect how BMI is interpreted?

The formula is the same for all adults, but interpretation differs for children, teenagers, and older adults. This calculator is designed for adult use.

Should I see a doctor about my BMI result?

If your BMI falls outside the healthy range, it's worth discussing with a healthcare professional, who can assess your overall health far beyond this single number.