BMI Calculator
Calculate Body Mass Index from height and weight.
Assumptions used in this calculation
- Adult thresholds: Category cutoffs (18.5, 25, 30) are the WHO adult standard and are not adjusted for age, sex, or ethnicity; separate percentile-based charts apply to children.World Health Organization BMI classification
About this calculator
Working out BMI by hand means picking the right formula for your unit system, squaring a height value correctly, and remembering which threshold band you land in, a small enough hassle that most people just guess instead of checking. This calculator takes your weight and height, in either metric (kg/cm) or imperial (lb/in) units, and computes Body Mass Index using the standard formula: weight divided by height squared, with the imperial version scaled by 703. It then places the result into one of four WHO weight categories, underweight, normal, overweight, or obese, so you get an instant, standardized read on where your weight sits relative to your height. Because BMI is a simple ratio rather than a body-composition measurement, it can't distinguish muscle from fat, which is worth remembering when interpreting the category. Still, as a quick, consistent screening number, it's more reliable than eyeballing a scale reading alone, and it's the same formula doctors and public health agencies use as a starting point.
Worked example
70 kg, 170 cm
Result: BMI = 24.2 (Normal)
How to use this
- 1Enter your height and weight, in either metric or imperial units.
- 2Read your BMI value and which category it falls into (underweight, normal, overweight, obese).
Troubleshooting
My BMI seems off for my body type.
BMI doesn't account for muscle mass, so it can misclassify athletic or very muscular people, it's a general screening measure, not a diagnosis.
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