About the BMI Calculator
Body mass index is the quick screening number that health services around the world use to relate weight to height, and this BMI calculator gives you yours in seconds. Choose metric or imperial units, enter your current weight and height, and your BMI appears instantly to one decimal place, together with its standard weight category: underweight, normal, overweight or obese.
The categories follow the widely used WHO thresholds — 18.5, 25 and 30 — so your result is directly comparable with what a doctor's office or health questionnaire would report. Because BMI involves personal health data, it matters that this tool runs entirely in your browser: your numbers are never uploaded, no account is needed, and the result updates the instant you type.
Features
- Metric (kg, cm) and imperial (lb, in) units
- BMI shown instantly to one decimal place
- WHO weight category displayed with the score
- Same formula used by health services worldwide
- No sign-up and no data uploaded
- Works on any device, even offline
How to calculate your BMI
- Choose metric or imperial units.
- Enter your weight in kilograms or pounds.
- Enter your height in centimetres or inches.
- Read your BMI and its weight category.
Frequently asked questions
How is BMI calculated?
In metric units, BMI is weight in kilograms divided by height in metres squared: kg ÷ m². In imperial units the equivalent is 703 × pounds ÷ inches². For example, 70 kg at 175 cm gives 70 ÷ 1.75² = 22.9. This calculator applies whichever formula matches your chosen units.
What is a healthy BMI range?
For adults, the WHO classifies a BMI of 18.5 to 24.9 as the normal range. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is obese. These cut-offs are population-level screening bands rather than individual diagnoses, but they are the standard reference worldwide.
Is BMI accurate for athletes and muscular people?
BMI cannot distinguish muscle from fat, so muscular athletes often score as overweight despite low body fat, and it can also underestimate fat in people with little muscle mass. If that describes you, pair BMI with a body-fat estimate — Tooldoodle's body fat calculator uses tape measurements — for a fuller picture.
Is BMI calculated differently for men and women?
No — the adult formula and WHO categories are identical for men and women. Children and teenagers are different: their BMI is interpreted against age- and sex-specific growth percentiles rather than fixed thresholds, so this adult calculator is not suitable for anyone under 18.
Is my BMI result medical advice?
No. BMI is a rough screening estimate and this tool is for information only — it cannot account for muscle mass, age, ethnicity, pregnancy or individual health factors. Talk to a doctor or qualified health professional before making decisions about your weight or health based on any calculator.