BMI Formula (Body Mass Index)
Calculate Body Mass Index using BMI = weight/height².
Includes both metric and imperial formulas with BMI category ranges.
The Formula
Metric
Imperial
BMI is a simple screening tool that estimates body fat based on weight and height.
It is widely used as a quick health indicator, though it does not measure body fat directly.
Variables
| Symbol | Meaning |
|---|---|
| BMI | Body Mass Index (kg/m²) |
| weight | Body weight in kilograms (kg) or pounds (lbs) |
| height | Height in metres (m) or inches (in) |
| 703 | Conversion factor for imperial units |
BMI Categories
| BMI Range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 - 24.9 | Normal weight |
| 25.0 - 29.9 | Overweight |
| 30.0 and above | Obese |
Example 1 (Metric)
A person weighs 75 kg and is 1.78 m tall. What is their BMI?
BMI = weight / height²
BMI = 75 / (1.78)²
BMI = 75 / 3.1684
BMI ≈ 23.7 — Normal weight
Example 2 (Imperial)
A person weighs 185 lbs and is 5'10" (70 inches) tall. What is their BMI?
BMI = (weight × 703) / height²
BMI = (185 × 703) / (70)²
BMI = 130,055 / 4,900
BMI ≈ 26.5 — Overweight
When to Use It
Use the BMI formula when you need a:
- Quick general screening of weight status
- Starting point for health assessments
- Population-level health comparisons
BMI has limitations. It does not distinguish between muscle and fat.
Athletes or muscular individuals may have a high BMI but low body fat.
For a more complete picture, consider body fat percentage and waist-to-hip ratio.
This formula is for general educational purposes only. It is not medical advice. Consult a healthcare professional for personal health assessments.