How to Calculate BMI Correctly
Body Mass Index (BMI) is a simple screening tool used worldwide to estimate whether your weight is in a healthy range for your height.
The BMI formula
BMI is calculated by dividing your weight in kilograms by the square of your height in meters:
BMI = weight (kg) ÷ height (m)²
For imperial units, the equivalent formula is:
BMI = (weight in lbs ÷ height in inches²) × 703
Example: A person weighing 70 kg and 1.75 m tall has BMI = 70 ÷ (1.75 × 1.75) = 22.9.
BMI categories
- Underweight: BMI below 18.5
- Normal weight: BMI 18.5 – 24.9
- Overweight: BMI 25 – 29.9
- Obese: BMI 30 or above
These ranges apply to most adults. Children and teens use age- and sex-specific percentile charts instead.
Limitations of BMI
BMI does not distinguish between muscle and fat. Athletes with high muscle mass may have a higher BMI without excess body fat. It also does not account for age, sex, bone density, or fat distribution. For a fuller picture, consider pairing BMI with waist circumference or a body fat calculator.
Try our free BMI calculator
Skip the manual math — our BMI Calculator supports kg/lbs and cm/ft-in, shows your category instantly, and includes variations for men, women, and kids.