Body Mass Index (BMI) is a number calculated from your weight and height. It is used as a screening tool to identify potential weight-related health risks. WHO classifies BMI into four categories: underweight (<18.5), normal weight (18.5–24.9), overweight (25–29.9), and obese (≥30).

Is this BMI calculator completely free?

Yes. The tool is free to use with no registration, no account, and no payment required.

Do I need an account to use this BMI calculator?

No. Open the page and start calculating immediately. Nothing is stored or logged.

What is the difference between metric and imperial BMI?

The formula is the same: BMI = weight(kg) / height(m)². Metric uses kg and cm directly; imperial inputs (lbs, feet, inches) are converted to metric before the calculation.

BMI calculator

BMI calculator is a health tool that computes your Body Mass Index using the WHO formula. It accepts metric and imperial units, classifies the result into the four WHO categories, and shows the healthy weight range for your height on a colour-coded scale. The tool runs in your browser.

Height (cm)

Weight (kg)

Dedicated pages

Unit-specific and demographic BMI calculators.

BMI calculator, metric (kg / cm)

Calculate your Body Mass Index using kilograms and centimetres. Instant WHO weight category result. Free. Runs in your browser.

BMI calculator, imperial (lbs / ft in)

Calculate your Body Mass Index using pounds and feet/inches. Instant WHO weight category result. Free. Runs in your browser.

BMI calculator for women

Calculate your BMI as a woman. See your WHO category and healthy weight range for your height. Free, runs entirely in your browser.

BMI calculator for men

Calculate your BMI as a man. See your WHO category and healthy weight range for your height. Free, runs entirely in your browser.

How to calculate your BMI

Choose your unit system, metric (kg / cm) or imperial (lbs / ft).
Enter your height and weight in the input fields.
Your BMI, WHO category, and healthy weight range appear instantly.
Use the colour bar to see where your BMI falls across the four WHO categories.

Common uses

Checking whether your weight is in the healthy range for your height
Tracking BMI changes over time during weight loss or gain alongside a calorie calculator
Estimating your healthy weight target range before starting a diet or fitness programme

Technical specification

Algorithm or formula: WHO Body Mass Index: BMI = weight(kg) / height(m)^2. Classification thresholds (underweight < 18.5, normal 18.5 to 24.9, overweight 25 to 29.9, obese ≥ 30) follow WHO Technical Report Series 894 (2000).
Browser API or library: Pure JavaScript arithmetic. No external library.
Input limits: Numeric inputs only. Imperial values are converted to kg and m before the calculation. No upper bound enforced.
Output: BMI value to one decimal place, WHO category label, and the healthy-weight range for the entered height.
Known limitations: BMI is a population-level screening tool, not a diagnosis. Muscular individuals, pregnant people, and children under 18 are commonly excluded from standard BMI thresholds.

Frequently asked questions

What is BMI?: Body Mass Index (BMI) is a number calculated from your weight and height. It is used as a screening tool to identify potential weight-related health risks. WHO classifies BMI into four categories: underweight (<18.5), normal weight (18.5–24.9), overweight (25–29.9), and obese (≥30).
Is this BMI calculator completely free?: Yes. The tool is free to use with no registration, no account, and no payment required.
Do I need an account to use this BMI calculator?: No. Open the page and start calculating immediately. Nothing is stored or logged.
What is the difference between metric and imperial BMI?: The formula is the same: BMI = weight(kg) / height(m)². Metric uses kg and cm directly; imperial inputs (lbs, feet, inches) are converted to metric before the calculation.

Reviewed and tested May 25, 2026.