Enter your height and weight to find your Body Mass Index (BMI) and the range it falls into. BMI is a general guide only – it does not measure body fat and it is not a medical diagnosis.
BMI Calculator
Your BMI:
General category:
BMI is a general guide only and does not measure body composition. For personal health advice, please speak to a health professional.
Read more about what the ranges mean in our guide: How to Work Out Your BMI
How to use the BMI Calculator
- Choose your units at the top: “Metric — kg and cm” or “Imperial — pounds, feet and inches”.
- If you picked metric, enter your height in centimetres and your weight in kilograms.
- If you picked imperial, enter your height in feet and inches, and your weight in pounds.
- Press “Calculate BMI”.
- Read your BMI number and the general category shown under it.
How it works
BMI stands for Body Mass Index. The formula is: BMI = weight in kilograms ÷ (height in metres × height in metres). Height is squared because the measure is meant to account for body size as you scale up in both directions, not just one. If you use imperial units, the tool converts pounds to kilograms and feet and inches to metres first, then applies the same formula.
You enter your height and weight, the calculator does the division, and it shows your BMI rounded to one decimal place. Underneath, it places your result in one of four general bands used for adults: below 18.5 is classed as underweight, 18.5 to 24.9 as normal, 25 to 29.9 as overweight, and 30 or above as obese. Treat the band as a rough guide: BMI does not measure body fat directly, and cannot tell muscle from fat.
Worked example
Take an adult who is 175 cm tall and weighs 70 kg. Enter 175 in the height (cm) box and 70 in the weight (kg) box, with metric units selected.
First the height in metres: 175 cm is 1.75 m, and 1.75 × 1.75 = 3.0625. Then the division: 70 ÷ 3.0625 = 22.9, rounded to one decimal place. That is the BMI the calculator shows, and because 22.9 sits between 18.5 and 24.9, the category shown is Normal.
Common mistakes
- Typing your height in metres into the centimetres box. The box expects 175, not 1.75 — entering 1.75 produces a wildly wrong result.
- Mixing the unit systems, such as weighing yourself in pounds but leaving the tool set to kilograms.
- Weighing yourself at different times of day and comparing the results. Weight shifts during the day with food and drink, so weigh at the same time, ideally in the morning, for a fair comparison.
- Reading too much into one number if you are very muscular. Muscle is denser than fat, so a strong, fit person can land in the overweight band while carrying little body fat.
Frequently asked questions
Q: Is BMI the same for children and teenagers?
No. The four bands on this page are for adults. Children and teenagers are assessed with growth charts that compare them with others of the same age and sex, so a child’s BMI is read differently. A health professional can interpret it properly.
Q: My BMI is just outside the normal band. Should I worry?
A result near a boundary is not a verdict on your health. BMI is one rough measure among many, and things like waist size, fitness, blood pressure and family history all matter too. If you are concerned, it is worth a conversation with a doctor rather than a decision based on a single number.
Q: How often should I check my BMI?
There is little value in checking daily, because small daily weight changes are mostly water. Checking every few weeks, at the same time of day and on the same scales, gives you a steadier picture of the trend.