BMI Calculator
Body Mass Index in either metric or imperial units.
Last updated: January 2025 · Built for the 2024–25 financial year
Inputs
Results
Your BMI
24.2
Category
Healthy weight
< 18.5
Under
Under
18.5–24.9
Healthy
Healthy
25–29.9
Over
Over
30+
Obese
Obese
Results are estimates only. For financial advice, consult a licensed adviser.
Overview
Body Mass Index for adults — WHO categories
Body Mass Index relates weight to height. Designed by Adolphe Quetelet in 1832 and adopted by the WHO in 1995, it is a population-level screening tool — fast and free, but blind to muscle, frame and ethnicity.
BMI is the first metric a GP uses, but it should never stand alone. Pair it with waist circumference (>94 cm men, >80 cm women is elevated risk) and body-fat percentage for a full picture.
Formula
BMI in metric units
BMI = weight (kg) ÷ height (m)²
For imperial: BMI = 703 × weight(lb) ÷ height(in)².
Worked example
Adult, 78 kg, 1.78 m tall
- Height² = 1.78 × 1.78 = 3.1684.
- BMI = 78 ÷ 3.1684.
- BMI = 24.6 — upper end of healthy range.
Answer: BMI 24.6 (Healthy weight)
WHO BMI categories
| Range | Category |
|---|---|
| < 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obese class I |
| 35.0 – 39.9 | Obese class II |
| ≥ 40 | Obese class III |
Pro tips
- •Athletes with high muscle mass often score 'overweight' — that's normal.
- •Asian populations carry health risk at lower BMIs (~23 cutoff).
- •Track waist-to-height ratio (<0.5) alongside BMI.