How to use the bmi calculator
- Choose metric or imperial units.
- Enter your height and weight. Sliders let you explore quickly.
- Read your BMI, the category it falls into and the healthy weight range for your height.
- Copy the summary if you want to keep a record.
Features
- Metric and imperial inputs with exact unit conversion (1 in = 2.54 cm, 1 lb = 0.45359237 kg)
- WHO adult categories from underweight to obesity class III
- Healthy weight range (BMI 18.5–24.9) for your height
- How far your weight is from the healthy range
- Formula shown with your own numbers; nothing is uploaded
The BMI formula and categories
BMI = weight in kilograms ÷ (height in metres)². Example: 70 kg and 175 cm gives 70 ÷ 1.75² = 22.9. The World Health Organization classifies adult BMI as underweight below 18.5, normal weight 18.5 to 24.9, overweight 25 to 29.9, and obesity class I (30–34.9), II (35–39.9) and III (40 and above).
The healthy weight range is found by reversing the formula: 18.5 × height² to 24.9 × height². For 175 cm that is 56.7 kg to 76.3 kg.
What BMI does and doesn't tell you
BMI is a quick population-level screening number. It does not measure body fat, where fat is stored, or fitness. Muscular people can have a high BMI with little body fat, older adults can have a normal BMI with low muscle mass, and the same BMI carries different risk levels across ethnic groups: several Asian health bodies use lower cut-offs (overweight from 23, obesity from 25) for South Asian populations.
BMI should not be used for children and teenagers (they use age- and sex-specific percentile charts), during pregnancy, or for athletes. This tool is not medical advice; a doctor will also look at waist circumference, blood pressure, blood tests and history.