BMI calculator for adults
Enter your height and weight and this BMI calculator shows your body mass index, its category and the healthy weight range for your height.
Last updated
How to use the BMI calculator
- Enter your height in centimetres.
- Enter your weight in kilograms.
- Press Calculate BMI.
- Read your BMI, its category and the normal weight range for your height.
How the BMI calculator works
Body mass index compares your weight with your height. It was designed as a quick way to screen large groups of people, and doctors still use it as a first check because it needs only two measurements.
BMI is only a screening number. It cannot tell muscle from fat, so athletes can score as overweight, and it ignores age, sex and where fat is stored. Treat it as a starting point for a conversation with a doctor, not as a diagnosis.
Formula
BMI = weight in kg ÷ (height in metres)². Divide your height in centimetres by 100 to get metres.
Adult categories: under 18.5 is underweight, 18.5 to 24.9 is normal, 25 to 29.9 is overweight, and 30 or above is obese. The normal weight range for a height runs from 18.5 × height² to 24.9 × height².
Example
For a height of 170 cm and a weight of 70 kg, the height in metres is 1.70 and 1.70² is 2.89. BMI = 70 ÷ 2.89, or about 24.2, which falls in the normal range.
At 170 cm the normal range runs from 18.5 × 2.89 ≈ 53.5 kg up to 24.9 × 2.89 ≈ 72.0 kg.
Tips and common mistakes
Measure without shoes
Shoes add a few centimetres of height, which lowers your BMI. Weigh yourself in light clothing at the same time of day.
Converting from feet and pounds
This calculator uses metric units. Use our unit converter to turn inches into centimetres and pounds into kilograms: one inch is exactly 2.54 cm and one pound is about 0.4536 kg.
Children need a different chart
For under-18s, BMI is compared with age- and sex-specific growth charts, so these adult categories don't apply.
Follow the trend, not one reading
A single number matters less than the direction over several months. The percentage calculator shows a weight change as a percent, which is how progress is often discussed.
Look beyond BMI
Waist size, activity and how you feel day to day add useful context. A doctor can weigh all of these together.
Frequently asked questions
Is BMI accurate?
It is a useful screening tool for groups but can mislead for individuals, especially very muscular people, older adults and some ethnic groups.
What is a healthy BMI?
For most adults, a BMI from 18.5 to 24.9 is considered the normal range.
Is BMI different for men and women?
The formula and adult categories are the same for both. Body composition differs, which is one reason BMI is only a first check.
Can I enter feet and pounds?
This calculator uses centimetres and kilograms. Convert your measurements first, then enter the metric values.
Is my data stored?
No. The calculation happens in your browser and nothing is saved or sent anywhere.