Calculate Your BMI: A Simple Guide to Body Mass Index

Body Mass Index (BMI) is a quick, standardized way to assess weight relative to height. It's calculated the same way worldwide and used as a screening tool—not a diagnosis.

Step-by-Step Calculation

Metric Method (Preferred)

1. Weigh yourself in kilograms (kg).
2. Measure height in meters (m).
3. Square your height (multiply by itself).
4. Divide weight by height squared.

BMI = weight (kg) ÷ [height (m)]²

Imperial Method

1. Weight in pounds (lb).
2. Height in inches (in).
3. Square height in inches.
4. Divide weight by height squared, then multiply by 703.

BMI = [weight (lb) ÷ height² (in²)] × 703

Worked Example

Person: 70 kg, 1.70 m

Height² = 1.70 × 1.70 = 2.89
BMI = 70 ÷ 2.89 = 24.2

Result: 24.2 → Normal weight (18.5–24.9)

BMI Classification (WHO)

Category	BMI (kg/m²)
Underweight	< 18.5
Normal weight	18.5 – 24.9
Overweight	25.0 – 29.9
Obesity Class I	30.0 – 34.9
Obesity Class II	35.0 – 39.9
Obesity Class III	≥ 40.0

Health Implications

• BMI ≥ 25: Increased risk of hypertension, type 2 diabetes, heart disease, stroke, certain cancers.
• BMI ≥ 30: Significantly higher risk; consider medical evaluation and structured intervention.
• BMI < 18.5: Risk of malnutrition, osteoporosis, immune dysfunction, hormonal issues.

Limitations & When to Use Other Tools

BMI does not measure body fat directly. Supplement with:

• Waist circumference
• Body fat percentage (DEXA, hydrostatic weighing, BIA)
• Clinical assessment by a healthcare provider

Quick tip: Use a reputable online BMI calculator (NIH, CDC, WHO) for instant results—just enter height and weight.