BMI Formula
BMI is simple to calculate by hand. Here is the formula in both metric and imperial units, with worked examples you can follow.
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Your BMI
22.9
Category
Healthy weight
Metric BMI formula
BMI = weight (kg) ÷ height (m)²
Example: a person weighing 70 kg at 1.75 m tall. Height squared is 1.75 × 1.75 = 3.0625. BMI = 70 ÷ 3.0625 = 22.9 — a healthy weight.
Imperial BMI formula
BMI = 703 × weight (lb) ÷ height (in)²
Example: 154 lb at 69 inches (5'9"). Height squared is 69 × 69 = 4761. BMI = 703 × 154 ÷ 4761 = 22.7.
Where does 703 come from?
703 is simply a unit-conversion factor. It converts the pounds-and-inches result so it matches the metric kg/m² scale, letting the same category thresholds apply to both systems.
Limitations of the formula
Because BMI uses only height and weight, it cannot distinguish muscle from fat, or show where fat is stored. Use it as a quick screen, not a diagnosis.
Frequently asked questions
How do I calculate BMI manually?
Divide your weight in kilograms by your height in metres squared. In imperial units, multiply your weight in pounds by 703, then divide by your height in inches squared.