How to use this BMI calculator
- Weight — enter your current weight in kilograms (kg).
- Height — enter your height in centimetres (cm).
- Read your BMI value and category — they update instantly as you type.
Nothing is submitted or stored: the numbers never leave your device, so you can check yours and your family's figures privately.
What is BMI and how is it worked out?
Body Mass Index is a simple ratio of weight to height. The formula is your weight in kilograms divided by your height in metres squared: BMI = kg ÷ (m × m). Because height is in metres, this calculator divides your centimetres by 100 first. BMI gives a quick, standardised number that lets you see roughly where your weight sits relative to your height, which is why doctors and health services use it as a first-pass screening measure.
BMI categories (adults)
- Underweight: below 18.5
- Normal weight: 18.5 – 24.9
- Overweight: 25 – 29.9
- Obese: 30 and above
These ranges come from the World Health Organization and apply to most adults aged 20 and over. Different thresholds are sometimes used for children, older adults, and some ethnic groups, so the bands above are a guide rather than a hard rule for everyone.
The limits of BMI — please read
BMI is a general indicator, not a measure of health. It cannot tell the difference between muscle and fat, so very muscular people (like athletes) can show a high BMI while carrying little fat, and others can sit in the "normal" range while still having an unhealthy amount of body fat. It also ignores where fat is stored, your age, sex, bone density and overall fitness. Use your BMI as a starting point for a conversation, not a verdict.
Medical disclaimer: This calculator is for general information only and is not medical advice. BMI alone cannot diagnose health or assess individual risk. Always consult a qualified doctor or healthcare professional before making decisions about your weight, diet or health.
Is it private?
Yes. The calculation runs entirely in your browser using plain JavaScript. Your weight and height are never uploaded, logged or sent to any server — there is no account and nothing to delete.
Frequently asked questions
How do I convert pounds and feet to kg and cm?
To get kilograms, divide your weight in pounds by 2.205. To get centimetres, multiply your height in inches by 2.54 (so 5 ft 7 in = 67 in ≈ 170 cm).
What's a "good" BMI?
For most adults a BMI between 18.5 and 24.9 is considered the normal range, but a single number can't capture your whole health picture — fitness, diet and body composition all matter.
Is my data uploaded?
No — everything is calculated on your device and nothing is sent anywhere.