How to Calculate BMI Average & Factors

Keeping a healthy body weight is a vital component of overall health. The National Heart, Lung and Blood Institute uses three metrics to determine whether a person is overweight: waist circumference, the presence of risk factors for obesity and the Body Mass Index, or BMI.

The BMI is a helpful but limited tool. Because it only looks at height and weight, it may overestimate the amount of body fat in very muscular people. However, as a general rule, the BMI can help make sure you're keeping your weight in check.

Things You'll Need

• Scale
• Tape measure
• Calculator
• Pen and paper

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Instructions

• 1

  Measure your weight in pounds on a scale, and your height in total inches using a tape measure. If you know your height in feet and inches, multiply the feet by 12 and add the inches.

• 2

  Use the calculator to multiply your weight in pounds by 703. Write down the resulting number.

• 3

  Clear the calculator and square the value you found for your weight. Some calculators have an "X squared" button; if yours doesn't, type in your weight in pounds, press the multiplication key and then press the equals sign. Write down the answer.

• 4

  Divide the first number (height x 703) by the second number (weight squared). The result is your BMI number as defined by the Centers for Disease Control.

• 5

  If this number falls below 18.5, you are underweight. If it is between 18.5 and 25, you are normal weight. If greater than 25 but less than 30, overweight. And if your BMI is 30 or greater, you are considered obese.