BMI (Body Mass Index) is a numerical value calculated from a person's weight and height that provides a general indicator of body fatness and weight categories.
Purpose
✔️ Screening tool for weight-related health risks
✔️ Population-level health assessment
✔️ Simple metric for tracking weight changes
1. BMI Formula
Calculation Method:
BMI = Weight (kg) ÷ [Height (m)]²
(or Weight (lbs) ÷ [Height (in)]² × 703 for imperial units)
Example:
Weight = 70 kg
Height = 1.75 m
BMI = 70 ÷ (1.75 × 1.75) = 22.86
2. Measurement Requirements
For Accuracy:
✅ Weight:
Measure in the morning after bathroom use
Use a calibrated digital scale (barefoot, light clothing)
✅ Height:
Stand straight against a wall (no shoes)
Use a stadiometer or rigid measuring tape
❌ Avoid:
Measuring after meals or exercise
Using approximate height/weight
3. BMI Categories (WHO Standard)
| BMI Range | Classification | Health Risk |
|---|---|---|
| <18.5 | Underweight | Nutritional deficiency |
| 18.5–24.9 | Normal weight | Low risk |
| 25–29.9 | Overweight | Moderate risk |
| ≥30 | Obesity | High risk |
Note: Athletes with high muscle mass may show falsely high BMI.
4. Tools for Measurement
Manual Calculation: Use the formula above
Online Calculators: WHO BMI Calculator
Smart Scales: With BMI function (e.g., Withings, Tanita)
5. Limitations of BMI
⚠️ Does Not Account For:
Muscle vs. fat distribution
Bone density
Age/gender differences (e.g., older adults lose muscle)
For Athletes: Combine with body fat % (DEXA scan or skinfold calipers).
Key Tip:
Recheck BMI monthly if adjusting weight for sports. For precise tracking, pair with waist circumference measurements.
(Source: WHO 2023, ACSM Guidelines for Exercise Testing)
