BMI Calculator
Calculate Body Mass Index (BMI) and category.
How BMI is calculated
Body mass index compares your weight with your height to place you in a broad weight category. It is the screening measure most clinics reach for first because it needs nothing but a set of scales and a tape measure. This BMI calculator takes weight in kilograms and height in centimetres and returns your index along with the category it falls in — underweight, normal, overweight or obese.
How to use the BMI Calculator
- Enter your Weight (kg).
- Enter your Height (cm) — the calculator converts to metres for you.
- Read your BMI and its category, which update as you type.
- Try a target weight to see what BMI it would give you.
Formula and a worked example
BMI = weight (kg) ÷ height (m)2
Height must be squared, which is why a small height error shifts BMI more than a small weight error does. In imperial units the same index is 703 × pounds ÷ inches², and the categories are identical.
Worked example
Someone 175 cm tall weighing 70 kg: 1.75² = 3.0625, and 70 ÷ 3.0625 = 22.86, which sits in the normal range. Adding 10 kg pushes the same person to 26.12 and into the overweight band.
BMI categories
- Below 18.5 — underweight
- 18.5 to 24.9 — normal weight
- 25.0 to 29.9 — overweight
- 30.0 and above — obese
Frequently asked questions
How do you calculate BMI?
Divide your weight in kilograms by your height in metres squared. For 70 kg at 1.75 m: 70 ÷ (1.75 × 1.75) = 22.86.
Is BMI accurate for everyone?
No. It cannot tell muscle from fat, so athletes often read as overweight while someone with low muscle mass may read as normal despite high body fat. It also shifts in meaning for children, pregnant women and older adults.
What is a healthy BMI?
For most adults, 18.5 to 24.9. Some health bodies use a lower upper limit for South Asian populations because risk rises at a lower index.
What should I use instead of BMI?
Waist measurement and body fat percentage give a fuller picture. Try our body fat calculator alongside this one.
Related calculators
Other tools people use alongside the BMI calculator.