BMI Calculator
Body-mass index with WHO category, BMI Prime and healthy weight range.
What it does
Body-mass index compares weight with height: BMI = kg / m². The result is placed in the WHO weight categories, with a healthy weight range for your height.
Where it's used
A quick general screening measure for adults.
How to use it
- Choose metric or imperial.
- Enter your weight and height.
- Read your BMI, category and healthy range.
The formula explained
- BMI
- weight (kg) ÷ height (m)²
- WHO bands
- under 18.5 · 18.5–24.9 normal · 25–29.9 overweight · 30+ obese
- BMI Prime
- BMI ÷ 25
Worked example
An adult who weighs 180 lb and is 5 ft 11 in tall.
Inputs:
- Units: Imperial (lb, ft/in)
- Weight: 180 lb
- Height — feet: 5 ft
- Height — inches: 11 in
The calculator gives:
- BMI: 25.1 kg/m²
- Category (WHO): Overweight
- BMI Prime: 1
Tips and common mistakes
- BMI does not tell muscle from fat — athletes can read “overweight”.
- Not designed for children, teenagers or pregnancy.
- For many Asian populations lower cut-offs (23 and 27.5) are used.
Questions people ask
What is a healthy BMI for adults?
The WHO ranges are: under 18.5 underweight, 18.5–24.9 healthy weight, 25–29.9 overweight and 30 or more obesity. The calculator also shows the weight range that would be healthy for your height.
What does BMI Prime mean?
BMI Prime is your BMI divided by 25, the top of the healthy range. 1.0 is exactly on that line, below 1.0 is under it, and 1.2 means 20 % above it.
How is BMI checked for children and teenagers?
Children are still growing, so their BMI is compared with growth charts for their age and sex (WHO or CDC percentiles) instead of the adult categories. Ask a doctor or school nurse to read it for a child.
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Enter your values to get the result with the formula, substituted values and an explanation of each step.