Step-by-Step Calculation
- Convert your height to meters (if using metric) or keep in inches (if using imperial).
- Square your height.
- Divide your weight in kg by that squared height (metric formula), or use the imperial formula with the 703 multiplier.
Worked Example
A person weighing 70 kg, standing 1.75 m tall:
BMI = 70 / (1.75 × 1.75) = 70 / 3.0625 = 22.9
That falls in the "Normal Weight" range (18.5–24.9). For an imperial example: 154 lbs at 5'9" (69 inches): BMI = (154 × 703) / (69 × 69) = 108,262 / 4,761 ≈ 22.7 — nearly identical, confirming the two formulas are just unit conversions of each other.
Frequently Asked Questions
Is BMI accurate for athletes?
Not particularly — muscular individuals often show a BMI in the "overweight" range despite having low body fat, since BMI cannot distinguish muscle mass from fat mass.
Does BMI apply the same way to children?
No — children and teens use age- and sex-specific BMI percentile charts rather than the fixed adult categories, since healthy body composition changes significantly during growth.
