How to Calculate BMI: A Step-by-Step Guide

Calculating your BMI takes less than a minute once you know the formula. You only need two measurements: your weight and your height. Here's how to do it in both metric and imperial systems.

Metric Formula (kg and meters)

BMI = weight (kg) ÷ height (m)²

1. Measure your height in meters (e.g., 1.70 m).
2. Multiply your height by itself: 1.70 × 1.70 = 2.89.
3. Divide your weight in kg by that number: 68 ÷ 2.89 = 23.5.
4. Your BMI is 23.5 — in the healthy range.

Imperial Formula (lbs and inches)

BMI = (weight in lbs ÷ height in inches²) × 703

1. Convert your height to total inches: 5 ft 7 in = 67 inches.
2. Multiply height by itself: 67 × 67 = 4489.
3. Divide weight by that: 150 ÷ 4489 = 0.0334.
4. Multiply by 703: 0.0334 × 703 = 23.5.

Worked Example

Person: 5 ft 9 in (175.3 cm), 180 lbs (81.6 kg). Using metric: 81.6 ÷ (1.753 × 1.753) = 81.6 ÷ 3.073 = 26.6. This falls in the 'overweight' category (25–29.9).

Use a Calculator to Save Time

Doing the math by hand works fine, but our BMI calculator handles both unit systems automatically. Just enter your height and weight and get an instant result with a full explanation of what your BMI means.