BMI Calculator
Calculate your Body Mass Index (BMI) instantly. Enter weight and height to see your BMI score, weight category, and healthy weight range. South African adult and child reference values.
How to Use the BMI Calculator
Enter your weight in kilograms and height in centimetres. The calculator instantly computes your BMI and shows your weight category. BMI is a quick screening tool used by healthcare professionals worldwide.
Use the Extended Calculator below for the Adult, Child, and Athlete tabs with a visual BMI gauge and historical trend tracking. The Professional Calculator adds ideal weight from 7 formulas, body composition estimates, and FFMI.
Historical BMI Trend
BMI Formula
Example: 75 kg ÷ (1.75 × 1.75) = 24.5 — Normal Weight.
BMI Categories (WHO)
| Category | BMI Range |
|---|---|
| Underweight | Below 18.5 |
| Normal Weight | 18.5 – 24.9 |
| Overweight | 25.0 – 29.9 |
| Obese Class I | 30.0 – 34.9 |
| Obese Class II | 35.0 – 39.9 |
| Obese Class III | 40.0+ |
Ideal Weight — 7 Formulas Compared
| Formula | Ideal Weight | Difference |
|---|---|---|
| Robinson (1983) | 68.9 kg | +9.1 kg |
| Miller (1983) | 68.7 kg | +9.3 kg |
| Devine (1974) | 70.5 kg | +7.5 kg |
| Hamwi (1964) | 72.0 kg | +6.0 kg |
| BMI-based (22) | 66.5 kg | +11.5 kg |
| Peterson (2016) | 67.7 kg | +10.3 kg |
| Lemmens (2005) | 67.4 kg | +10.6 kg |
| Average Ideal | 68.8 kg | +9.2 kg |
BMI Sensitivity Table (±10 kg)
| Weight | BMI | Category |
|---|---|---|
| 68 kg | 22.2 | Normal Weight |
| 73 kg | 23.8 | Normal Weight |
| 76 kg | 24.8 | Normal Weight |
| 78 kg (current) | 25.5 | Overweight |
| 80 kg | 26.1 | Overweight |
| 83 kg | 27.1 | Overweight |
| 88 kg | 28.7 | Overweight |
Body Composition Breakdown (Deurenberg estimate)
Formula: Body Fat % = 1.20 × BMI + 0.23 × Age − 10.8 × (1 if male, 0 if female) − 5.4
Your estimated body fat: 22.4%
Fat mass: 17.5 kg | Lean mass: 60.5 kg
This is a population-level estimate (±3–5%). For accurate body composition use DEXA, hydrostatic weighing, or skinfold calipers with a trained assessor.