How to Calculate BMI: Formula & Example

Calculate it step by step

In metric units, divide weight in kilograms by height in metres squared. Convert centimetres to metres before squaring. A height of 170 cm is 1.70 m, and its square is 2.89 m².

Worked example

For 70 kg and 170 cm: 70 ÷ (1.70 × 1.70) = 24.22145… . The displayed BMI is 24.22. Its unrounded value falls in the standard 18.5 to below 25 interval.

Using pounds and inches

Convert pounds to kilograms with 0.45359237 and inches to centimetres with 2.54, then use the same metric formula. The common shortcut, pounds ÷ inches² × 703, uses a rounded conversion factor and may differ slightly.

Rounding near a boundary

Classification uses full precision, not the displayed rounded number. A BMI of 24.999 can display as 25.00 while still being below 25. This is a rounding effect, not a different category rule.

BMI = kg ÷ (cm ÷ 100)²
70 ÷ (1.70 × 1.70) = 24.22145…