BMI Calculator
Body Mass Index (BMI) relates weight to height and is a quick screen for under- or overweight. It is widely used because it needs only a tape measure and a scale, though it cannot distinguish muscle from fat.
Enter your height and weight, and choose metric or imperial units. The calculator returns your BMI and the standard weight-status category it falls in.
It is the screen most doctors start with, but treat the single number as a prompt to look closer rather than a verdict on your health.
Enter your values to see the result.
How this is calculated
Body Mass Index relates weight to height with the formula BMI = weight (kg) ÷ height (m)². For imperial entries, the calculator first converts inches to centimetres and pounds to kilograms, then applies the same formula. The result is sorted into standard adult categories: under 18.5 is underweight, 18.5–24.9 is normal weight, 25–29.9 is overweight, and 30 or above is obese.
BMI is popular because it needs only a scale and a tape measure, and at a population level it correlates with health risk. It is a screening tool, not a diagnosis — a single number cannot tell you whether your weight is healthy for you personally.
The model deliberately ignores body composition. It cannot distinguish muscle from fat, so very muscular people can read as "overweight" without being unhealthy, and older adults can read as "normal" while carrying too little muscle. It also uses adult cut-offs, so it is not suitable for children (who use age- and sex-specific percentile charts), and it does not adjust for the different body-fat thresholds that some ethnic groups use. For a clearer picture of body composition, pair it with the body-fat or waist-to-height calculator.
Worked example
An adult who is 175 cm tall and weighs 70 kg.
- 1Height in metres = 175 ÷ 100 = 1.75 m.
- 2Height squared = 1.75 × 1.75 = 3.0625 m².
- 3BMI = 70 ÷ 3.0625 ≈ 22.9 — within the normal weight range.
Frequently asked questions
- What is a healthy BMI range?
- For most adults, a BMI between 18.5 and 24.9 is considered a healthy weight. Below 18.5 is underweight, 25–29.9 is overweight, and 30 or above is obese.
- Is BMI accurate for muscular people?
- No. BMI does not separate muscle from fat, so very muscular individuals can read as “overweight” without being unhealthy. Use body-fat percentage for a clearer picture in those cases.
- Is BMI suitable for children?
- Children are assessed on age- and sex-specific percentile charts, not the adult categories. This calculator is intended for adults aged 18 and over.
- Is BMI accurate for muscular people?
- No. BMI does not separate muscle from fat, so very muscular individuals can read as "overweight" without being unhealthy. Use body-fat percentage or waist-to-height ratio for a clearer picture in those cases.
- Is BMI suitable for children?
- Children are assessed on age- and sex-specific percentile charts, not the adult categories. This calculator is intended for adults aged 18 and over.
Related calculators
Method: WHO standard BMI formula and adult cut-offs. No external data source. Last updated: September 2026.
These results are general estimates from established formulas and are not medical advice. They depend on the accuracy of the values you enter and on individual factors the formulas cannot capture. Consult a qualified healthcare professional before making decisions about your diet, training or treatment.