How to Calculate Body Fat & Percentage of Weight Lost

There are two ways to determine the amount of body fat you have: the body mass index (BMI) and percentage of body fat. BMI is the standard used by the World Health Organization to classify adults as underweight, overweight and obese. The U.S. Navy and U.S. Army developed a percentage of body fat formula. Calculating the percentage of weight you have lost, however, is simple and requires no complex formula.

Things You'll Need

• Tape measure
• Scale
• BMI calculator (available online)

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Instructions

• 1

  Calculate your BMI. Measure your height, and weigh yourself. Enter your height in feet and inches into a BMI calculator. You will find one in the Resources section. Enter your weight. Click "Compute BMI." If your BMI is under 18.5, you are underweight; if it is 18.5 to 24.9, you are of normal weight; 25 to 29.9, overweight; and 30 or greater, obese.

• 2

  Calculate your body fat percentage. See Resources for calculator. Enter your gender. Using the tape measure, measure yourself at your waist's narrowest point and enter that number. Do the same for your waist at your navel, your hip's widest point and your neck's narrowest point. Enter your height and your weight, and click "Calculate." For women between 20 and 40, 19 to 26 percent body fat is considered good to excellent. For age 40 to 60 or older, 23 to 30 percent is good to excellent. For men ages 20 to 40, 10 to 20 percent is good to excellent; for ages 40 to 60 or older, 19 to 23 percent is good to excellent.

• 3

  Use simple math to calculate the percentage of weight lost. Subtract your current weight from your original weight. Divide the result by your original weight. That number equals the percentage of weight lost.

  For example, if you used to weigh 135 pounds and lost 15 pounds, you now weight 120. 135 -- 120 = 15. 15/135 = 0.11. The amount of weight you lost is 11 percent of your original body weight.