BMI Calculator

The BMI calculator gives your Body Mass Index — a clinical screening measure used by doctors and public health systems worldwide to flag potential weight-related health risks. Enter height and weight in metric or imperial units for an instant reading and WHO category. Consult a healthcare professional for personalised health advice before making any changes to your diet or exercise routine. BMI is widely used as a first-pass health screen precisely because it requires only two inputs that everyone knows: height and weight. General practitioners, occupational health services, and insurance assessments all routinely record BMI as a baseline indicator. Understanding where you fall on the scale — and what it means — helps you have more informed conversations with your doctor. It is equally important to understand what BMI does not measure. It says nothing about body fat distribution, cardiovascular fitness, blood pressure, or metabolic health. Two people with the same BMI can have very different health profiles. Athletes with high muscle mass frequently register as overweight. Older adults with low muscle mass may read as normal weight despite elevated body fat. BMI is best treated as one data point among several, not a standalone verdict on health.

How to Use the BMI Calculator

The BMI Calculator is designed to give you an accurate answer in seconds. Follow these steps:

1. Step 1: Select your unit system using the toggle — metric (kilograms and centimetres) or imperial (pounds and feet/inches).
2. Step 2: Enter your weight. For metric, enter kilograms (e.g. 75). For imperial, enter pounds (e.g. 165).
3. Step 3: Enter your height. For metric, enter centimetres (e.g. 175). For imperial, enter feet and inches separately (e.g. 5 feet 9 inches).
4. Step 4: Your BMI score, WHO category (Underweight, Normal weight, Overweight, or Obese), and a visual scale appear instantly.

No account or sign-up required. All calculations run locally in your browser — nothing is stored or transmitted to any server.

How It Works

BMI = Weight (kg) ÷ Height² (m²) | Imperial: BMI = (lbs ÷ inches²) × 703

Formula: BMI = Weight (kg) ÷ Height² (m²) The formula was developed by Belgian mathematician Adolphe Quetelet in the 1830s and adopted as a clinical standard by Ancel Keys in 1972. Weight in kilograms is divided by height in metres, squared. Example: 75 kg, 1.75 m tall. BMI = 75 ÷ (1.75 × 1.75) = 75 ÷ 3.0625 = 24.5 → Normal weight WHO classification thresholds for adults: Under 18.5 — Underweight 18.5 to 24.9 — Normal weight 25.0 to 29.9 — Overweight 30.0 and above — Obese For imperial units the adjusted formula is: BMI = (Weight in lbs ÷ Height in inches²) × 703. BMI does not distinguish between muscle mass and body fat, and has known limitations for athletes, older adults, and some ethnic populations. Use it as a starting point, not a diagnosis. Research context: large population studies have found that all-cause mortality risk is lowest at BMI 22–27 — slightly wider than the "normal" band of 18.5–24.9 suggests. For people of South and East Asian descent, several health authorities recommend adjusted thresholds: overweight at 23.0 and obese at 27.5, because metabolic risk factors such as type 2 diabetes and hypertension tend to appear at lower BMI values in these populations. If your ethnic background is relevant, ask your doctor which thresholds are appropriate for your assessment.

Frequently Asked Questions