-
Step 1
+ Method 1 +
Using inches, measure your waist circumference at the navel, and call this number X. Measure your weight in lbs, and call this number Y. Your lean body mass is given by the formula
LBM = 94.42 - 4.15X + 1.082Y
And your total body fat is given by the equation
TBF = Y - LBM
That is, just subtract lean body mass from weight. -
Step 2
To calculate your percent body fat with the first method, simply divide your total body fat by your weight.
-
Step 3
For example, a 170 pound man has a waist measurement of 35 inches. Using the formulas above, his lean body mass is 133.11 lbs, and his total body fat is 36.89 lbs. His percent body fat is thus 36.89/170 = .217, or 21.7%.
-
Step 4
+ Method 2 +
The next method was developed by the US Navy to measure body density and percent body fat. To use it, you will need a calculator with the log function. First, measure your height, and waist and neck circumferences in inches. Call these quantities H, W, and N respectively. -
Step 5
The original Navy formulas were devised for metric measurements, but these two equations have been adjusted for inches. Your body density, BD, is computed as follows:
BD = 1.01774 - .19077LOG(W-N) + .15456LOG(H)
And your percent body fat is then:
%BF = 495/BD -450 -
Step 6
For example, if the same man is 71 inches tall, has a 35 inch waist, and a 18 inch neck, then H=71, W=35, and N=18. And so
BD = 1.01774 - .19077LOG(17) + .15456LOG(71)
= 1.01774 - .23473 + .28613
= 1.06914
His percent body fat is 495/1.06914 - 450 = 12.99, or about 13% -
Step 7
As you can see, the first method and the Navy method give different results. For this example, consider the 13%-21.7% to be the approximate range of percent body fat.
If you calculate your percent body fat over a period of time, use the same formula each time to track changes.
