Lean body mass is the weight of everything in your body other than fat. You can calculate your lean body mass from a few gender-specific body measurements. You may then convert your lean body mass to your body fat percentage. Body fat percentage is the percentage of your total body weight that comes from fat. It’s generally a more meaningful measure of fitness than your total body weight, since it distinguishes between the muscle and fat in your body.
Step 1
Take body measurements in inches with a tape measure. Measure your waist at the navel regardless of your gender. Women must also measure their forearm, wrist and hips at their fullest points.
Step 2
Weigh yourself in pounds with a bathroom scale. Perform this measurement when your water weight is its lowest level of the day, usually when you first wake up.
Step 3
Calculate the lean body mass for males. Professional bodybuilder and author Dave Draper recommends this formula: (total weight x 1.082) - (waist measurement x 4.15) + 94.42.
Let your waist measurement be 34 inches and your total weight be 187 lbs. for this example. Your lean body mass is (187 x 1.082) - (34 x 4.15) + 94.42 = 156 lbs.
Step 4
Compute the lean body mass for females. Draper recommends this formula: (total weight x 0.732) - (waist measurement x 0.157) + (forearm measurement x 0.434) + (wrist measurement / 3.14) - (hip measurement x 0.249) + 8.987.
Assume for this example that you have a 132 lbs. body weight, 31-inch waist, 9.5-inch forearm, 7-inch wrist and 39-inch hips. Your lean body mass is (132 x 0.732) - (31 x 0.157) + (9.5 x 0.434) + (7 / 3.14) - (39 x 0.249) + 8.987 = 97 lbs.
Step 5
Convert your lean body mass to your body fat percentage with this equation: (total weight - lean body mass) / (body weight) x 100.
Let your total weight be 187 lbs. and your lean body mass be 157 lbs. Your body fat percentage is (187 - 156) / (187) x 100 = 16.6 percent.
Things You'll Need
- Tape measure
- Bathroom scale
- Calculator
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