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How to use the BMI calculator
Choose metric or imperial units and enter your weight and height. Switching units converts the numbers you already entered, so you stay on the same person. The result shows your BMI, its category and the healthy weight range for your height.
How BMI is calculated
Body mass index is your weight in kilograms divided by your height in meters, squared. In imperial units the formula is weight in pounds × 703 ÷ height in inches squared.
Example: 72 kg and 175 cm. The height in meters is 1.75, and 1.75² = 3.0625. BMI = 72 ÷ 3.0625 ≈ 23.5. For 175 cm, the healthy range runs from 18.5 × 3.0625 ≈ 56.7 kg to 24.9 × 3.0625 ≈ 76.3 kg.
The adult categories
| BMI | Category (WHO, adults) |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Healthy range |
| 25.0 to 29.9 | Overweight |
| 30.0 and above | Obesity range |
What BMI cannot tell you
BMI is a quick screening number. It does not measure body fat, so muscular people can have a high BMI without excess fat. It does not show where fat is carried, and waist size is often a useful addition. Older adults and some ethnic groups can carry health risks at different BMI levels. A BMI result is a starting point for a conversation with a health professional, not a diagnosis.
Questions about BMI
Does BMI work for children?
Not with the adult categories. For children and teenagers, BMI is compared with age and sex percentile charts, which a doctor or pediatrician can interpret.
Is BMI accurate for athletes?
Not always. Muscle weighs more than fat, so a very muscular person can score in the overweight range while having a low body fat percentage.
What BMI is healthy?
For most adults, the World Health Organization calls 18.5 to 24.9 the healthy range. Being in that range does not guarantee good health. Blood pressure, blood sugar, fitness and diet matter too.