Body mass index, or BMI, is a number calculated from a person's height and weight. This number usually gives an accurate description of body composition, though certain populations such as athletes and bodybuilders have an inaccurate number due to increased muscle mass. BMI is often used to determine if an individual has a weight problem.
Step 1
Measure your height. Your BMI is calculated in meters, not feet and inches. To convert your height from feet and inches to meters, multiply your height in inches by 0.0254. Multiply your height in meters by itself, or squared. For example, if you are 70 inches tall, your height in meters is 1.778. Multiply 1.778 by 1.778 to get 3.161. This number will be the denominator, or bottom of the fraction.
Step 2
Measure your weight. The ideal time to do this is first thing in the morning. Convert your weight from pounds to kilograms. Divide your weight in pounds by 2.2. For example, if you weigh 170 pounds, your mass in kilograms is 77.272. This number is the numerator, or top of the fraction.
Step 3
Divide the numerator by the denominator to come up with your BMI number. For example, 77.272 / 3.161 = 24.445. This can be rounded to 24.45, which falls in the "normal" weight category.
Tips and Warnings
- The BMI categories include underweight, 18.5 or less; normal weight, 18.5-24.99; overweight, 25-29.99; obese, class 1: 30-34.99; obese, class 2, 35-39.99; and morbidly obese, 40 or higher.
- Only a doctor can determine if you are underweight, overweight or obese.
Things You'll Need
- Scale
- Calculator
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