BMI calculator guide
BMI is weight in kilograms divided by height in metres squared. It is a convenient population-level screening measure.
The result does not directly measure body fat and should be interpreted with age, body composition, medical history, and other health information.
How to use the BMI calculator
- Choose units: Select metric or imperial inputs.
- Enter measurements: Provide a positive height and weight.
- Review the result: Use the category as a screening indicator, not a diagnosis.
Formula and variables
Convert inputs to kilograms and metres before dividing weight by height squared.
BMI = weight (kg) / height (m)²- W — Weight
- Body mass (kg)
- H — Height
- Standing height (m)
Adult metric example
A 70 kg adult is 1.75 m tall.
- Weight
- 70 kg
- Height
- 175 cm
- BMI = 70 / 1.75²
- BMI ≈ 22.9
Result: The calculated BMI is approximately 22.9.
This falls in the conventional healthy-weight screening range for adults.
Understanding your results
Adult screening ranges
Common adult screening ranges classify BMI below 18.5 as underweight, 18.5–24.9 as healthy weight, 25–29.9 as overweight, and 30 or more as obesity.
Assumptions
- The calculator uses adult BMI thresholds.
- Measurements are entered accurately and represent current body size.
Limitations
- BMI does not distinguish muscle from fat.
- Children and teenagers require age- and sex-specific percentiles.
- Medical decisions should use professional assessment.
Common mistakes
- Entering height in centimetres as metres.
- Treating a screening category as a diagnosis.
- Using adult cutoffs for children.
Practical use cases
Health screening
Use BMI as one data point when discussing weight-related health with a qualified professional.
Frequently asked questions
Is BMI a diagnosis?
No. BMI is a screening measure and does not diagnose body fatness or health.
Can athletes have a high BMI?
Yes. Higher muscle mass can increase BMI without indicating excess body fat.
Sources and review
- Adult BMI Calculator — Centers for Disease Control and Prevention. Accessed 2026-07-16.
Reviewed 2026-07-16.