BMI Calculator
Free BMI calculator with metric and imperial units. Get your body mass index, WHO weight category and the healthy weight range for your height — instantly and privately.
🔒 Your measurements are processed in your browser and never uploaded.
Free BMI Calculator
This free online BMI calculator works out your Body Mass Index from your height and weight in seconds. It supports both metric (cm, kg) and imperial (feet/inches, pounds) units, shows your World Health Organization (WHO) weight category on a colour-coded scale, and tells you the healthy weight range for your height. It’s completely free, requires no sign-up, and runs entirely in your browser — your measurements are never uploaded.
How to use the BMI calculator
- Choose your unit system: Metric (cm, kg) or Imperial (ft/in, lb).
- Enter your height and weight in the boxes shown.
- Optionally add your age and gender for context.
- Click Calculate BMI to see your number, category and healthy weight range.
- Check where your marker sits on the colour scale — blue, green, amber or red.
What is BMI and what do the numbers mean?
Body Mass Index (BMI) is a simple measure that compares your weight to your height. The formula is
weight in kilograms divided by height in metres squared (kg/m²). For imperial units you can
also use 703 × lb / in². The result places you in one of the standard WHO categories below:
| BMI range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese |
BMI is a useful screening tool, but it is not a diagnosis. It does not distinguish muscle from fat or account for where fat is stored, so very muscular people can score “overweight” while having low body fat. Use BMI as a quick guide, and speak to a doctor or dietitian for a full assessment of your health.
Frequently asked questions
Is this BMI calculator free and private?
How is BMI calculated?
703 × weight(lb) / height(in)². For example,
70 kg at 175 cm gives a BMI of about 22.9.