The body mass index (BMI) is a calculation that allows you to compare your weight to your height. Health care workers use it to quickly identify patients who may be underweight or overweight. The World Health Organization (WHO) lists weight classifications based on the BMI in metric units. This requires you to convert to metric units, because you typically take your height and weight measurements in English units.
Step 1
Weigh yourself in pounds, using a bathroom scale. Assume you weigh 142 lbs. for this example.
Step 2
Measure your height in inches with a tape measure. Assume you're 70 inches tall for this example.
Step 3
Compute your BMI in English units. This uses the formula BMI = w / (h x h), in which w is your weight and h is your height. A weight of 142 lbs. and a height of 70 inches provides a BMI of 142 / (70 x 70) = 0.029 pounds per square inch (lb./in.^2).
Step 4
Multiply by 703 to convert your BMI in lb./in.^2 to metric units of kilograms per square meter (kg/m^2.) A BMI of 0.029 lb/in^2 is therefore equal to 0.029 x 703 = 20.4 kg/m^2.
Step 5
Use your metric BMI to classify your weight according to the WHO system. The sample BMI of 20.4 kg/m^2 is within the normal range of 18.5 to 25 kg/m^2. A BMI below this range is considered underweight; a BMI between 25 and 30 kg/m^2 is pre-obesity. A BMI above the pre-obesity level is considered to be obese.
Things You'll Need
- Bathroom scale
- Tape measure
- Calculator
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