BMI Calculator
Calculate your body mass index from height and weight to check your BMI category, free and private in your browser.
Enter Values
Before you rely on this: General information only — not medical advice. Speak to a qualified health professional about anything affecting your health.
How to use this calculator
- Enter your weight and height using whichever units you prefer.
- Press Calculate to see your BMI and weight category.
- Compare your result against the standard ranges below.
How it works
Body Mass Index (BMI) estimates body fat from your weight relative to your height. It is calculated as weight in kilograms divided by height in metres squared: BMI = kg ÷ m².
The standard adult categories are: under 18.5 (underweight), 18.5–24.9 (healthy), 25–29.9 (overweight) and 30 or more (obese). BMI is a quick screen, not a diagnosis — it doesn't separate muscle from fat or account for age, sex and build.
Worked example
80 kg at 1.8 m tall. BMI = 80 ÷ (1.8 × 1.8) = 80 ÷ 3.24 = 24.7, which sits in the healthy range.
Common mistakes
- Entering height in centimetres without switching the unit — 180 cm, not 180 m.
- Treating BMI as body-fat percentage — it doesn't distinguish muscle from fat.
Tips
- Measure height without shoes and weight at a consistent time of day.
- BMI ranges differ for children and some ethnic groups.
Frequently asked questions
Is BMI accurate for athletes?
Not always. Very muscular people can show a high BMI despite low body fat, so treat it as a general guide alongside other measures.
What is a healthy BMI?
For most adults 18.5–24.9 is considered healthy, but a health professional can advise what's right for you.
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Cite this tool
Zerdly. (2026). BMI Calculator. Retrieved from https://www.zerdly.com/tools/bmi-calculator/
Tip: Enter any known values to calculate the remaining results.
Designed to run locally in your browser. Tool inputs are not intentionally stored by Zerdly unless stated otherwise.