How to Calculate Your Body Mass Index (BMI)

The Body mass index, or BMI, is a commonly accepted shortcut to determining whether you are at the optimum weight for your height. The BMI has the advantage of being easy to calculate but is limited in that different people have different proportions of body fat to lean muscle mass, which weighs more.

Difficulty: Easy

Instructions

1. Weigh yourself as accurately as possible. Since having food or drinks in your system can affect your weight, most people prefer to weigh themselves first thing in the morning. Step on the scale 3 times to determine the best average weight.

2. Convert your height to inches and square it. A 5-foot, 7-inch woman is 67-inches tall. Take 67 and multiply it by itself to get the square to get 4,489.

3. Divide your weight in pounds by the squared height total. For a 155 lb. adult, divide 155 by 4486 to get .0346.

4. Multiply that number, .0346 in the example, by 703 (which converts from pounds and inches into kilograms and meters). This number, 24.29, is the BMI index.

5. Determine your weight range. A BMI below 18.5 is underweight, between 18.5 and 24.9 is the normal range, 25.0 to 29.9 is overweight and over 30 is obese.

Tips & Warnings

• The BMI should be used only as a screening tool to get a general idea of your weight range. Before beginning a weight loss (or gaining) program, you should consult your physician for further testing and consultation.
• While the BMI is a good starting point, you should consider any particular circumstances that may affect your index such as more or less muscle mass than the average person.
• For adults over 20, the BMI is not sex specific. Children and teens should interpret their results using BMI charts for their sex and age.

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