ToolBirch

BMI Calculator

Body Mass Index with the standard WHO weight category.Calculators

BMI Calculator

Body Mass Index from metric or imperial inputs, with the standard WHO weight category.

BMI
22.9
Category (WHO)
Healthy weight

BMI is a rough population-level screening measure. It does not account for muscle mass, age or body composition and is not a medical diagnosis.

About this tool

BMI is one number from height and weight. Enter your measurements in kilograms and centimetres or pounds and feet/inches to get the value and the WHO category band, with the measurement's limits stated plainly.

How to use the BMI Calculator tool

  1. Pick the unit system. Metric (kg, cm) or imperial (lb, ft + in).
  2. Enter weight and height. Both fields accept decimals.
  3. Read the result. The BMI value and its WHO category, computed on your device.

Supported formats

Input

  • Weight and height in metric units
  • Weight and height in imperial units

Output

  • BMI value
  • WHO weight category

Inputs are validated before anything is processed. Invalid values and unsupported files are rejected with a clear error instead of failing silently.

Frequently asked questions

Which categories are used?

The WHO bands: under 18.5 underweight, 18.5–25 healthy, 25–30 overweight, 30+ obesity.

Is BMI accurate for athletes?

Not really. Muscle mass raises BMI without adding health risk; waist and body-composition measures are better for muscular people.

Is this medical advice?

No. BMI is a population-level screening number, not a diagnosis for an individual.

Do the unit systems agree?

Yes — imperial inputs are converted with exact factors before the same formula is applied.

Privacy

Everything you enter stays in this browser tab. There is no upload endpoint for tool inputs, no account, and no server-side copy of your text or files. Results are produced locally and disappear when you close the page.

No account is required and no file is ever uploaded. See the privacy policy for details about analytics and the limited data this site stores.

Known limitations

  • No adjustment for age, sex or muscle mass.
  • Children and pregnancy need specialised charts not offered here.
  • Category boundaries follow the WHO adult standard only.

Related tools

Other free tools from the same collection.

Age CalculatorExact age in years, months and days, plus a birthday countdown.Unit ConverterConvert length, mass, temperature and data units precisely.Discount CalculatorFinal price after a discount — or the original price before it.Percentage CalculatorWork out percentages, percentage of a value and percent changes.