BMI calculator

How to calculate your BMI

1. Choose your unit system: metric (kg / cm) or imperial (lbs / ft).
2. Enter your height and weight in the input fields.
3. Your BMI, WHO category, and healthy weight range appear instantly.
4. 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: Height 50 to 272 cm (1 ft 8 in to 8 ft 11 in, with inches below 12) and weight 2 to 650 kg (5 to 1,430 lbs). Values outside these ranges show a hint instead of a result. Imperial values are converted to kg and m before the calculation.
• Output: BMI value to one decimal place, WHO category label (assigned from that rounded value), 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 a healthy BMI range?

A BMI of 18.5 to 24.9 is classified as healthy weight by the World Health Organization. Below 18.5 is underweight; 25 to 29.9 is overweight; 30 or above is obese. Results are estimates for informational purposes only.

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.

Do I need an account to use this BMI calculator?

The calculator works without an account. Open the page and start calculating immediately. All calculations run in your browser. Our servers are not involved at any point.

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.