How to Calculate BMI: Formula, Examples and What It Means
Work out body mass index by hand in kilograms or pounds, see the adult BMI categories, find your healthy weight range and learn what BMI cannot tell you.
Body mass index, or BMI, is a quick way to compare weight with height. Doctors use it as a first screening number for adults. You can work it out with one division, and this guide shows how in both metric and imperial units.
The metric formula
BMI = weight in kg ÷ (height in m)²
For someone who weighs 60 kg and is 165 cm tall, first change the height to metres: 1.65 m. Square it: 1.65 × 1.65 = 2.7225. Then divide: 60 ÷ 2.7225 ≈ 22.0.
The imperial formula
BMI = 703 × weight in lb ÷ (height in inches)²
For 180 lb at 5 feet 10 inches, the height is 70 inches, and 70² = 4,900. So BMI = 703 × 180 ÷ 4,900 ≈ 25.8. The 703 converts pounds and inches to the same scale as kilograms and metres.
What the number means for adults
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Healthy weight |
| 25 to 29.9 | Overweight |
| 30 and above | Obesity |
So the first example, 22.0, sits in the healthy range, and the second, 25.8, is just into the overweight range.
Finding your healthy weight range
Turn the formula around: weight = BMI × height². At 1.65 m, the healthy range of 18.5 to 24.9 gives 18.5 × 2.7225 ≈ 50.4 kg up to 24.9 × 2.7225 ≈ 67.8 kg.
What BMI cannot tell you
- Muscle or fat. A muscular athlete can have a high BMI while carrying little fat.
- Where weight sits. Fat around the waist carries more health risk than the same weight elsewhere.
- Children and teenagers. They are measured against BMI-for-age charts, not the adult table.
- Different populations. Some health services use lower cut-offs for people of South Asian and East Asian background.
Tip BMI is a starting point, not a diagnosis. If your number worries you, talk to a doctor, who can look at waist size, blood pressure and other measures too.
Try it yourself: BMI CalculatorBody mass index in metric or imperial units, with the adult category and healthy weight rangeOpen →Common questions
What is a normal BMI?
For most adults, 18.5 to 24.9 is considered a healthy range.
Is BMI different for men and women?
The adult formula and categories are the same for both. Body fat at the same BMI usually differs, which is one of BMI's limits.
How do I convert my height to metres?
Divide centimetres by 100. 172 cm is 1.72 m.