Body Fat Percentage Calculator

The formula this calculator uses

BF% = 495 / (1.0324 - 0.19077 x log(waist - neck) + 0.15456 x log(height)) - 450 for men

waist (cm)

Circumference at the navel, measured in centimetres

neck (cm)

Circumference just below the larynx, in centimetres

hip (cm)

Widest circumference of the hips; used in the female equation only

height (cm)

Standing height in centimetres, without shoes

How to check the result by hand

1. 1

   Take the three circumferences in centimetres

   Measure the waist at the navel, the neck just below the larynx, and the hip at its widest point, with the tape snug but not compressing the skin. For the worked male case those are a height of 180 cm, a neck of 38 cm and a waist of 90 cm; the female case adds a 95 cm hip. Record each to the nearest half centimetre and measure at the same time of day each time, since a waist can move a centimetre between morning and evening.

2. 2

   Choose the equation that matches the sex

   Men use waist minus neck as the circumference term; women use waist plus hip minus neck. The two equations share a shape but not their constants, so using the wrong one is not a small error. The male form is calibrated around 1.0324 and the female form around 1.29579, and the coefficients on the circumference term differ by nearly a factor of two.

3. 3

   Take the base-10 logarithms

   The circumference term for the male case is 52, whose base-10 logarithm is 1.7160033436347992, and the logarithm of the 180 cm height is 2.255272505103306. The female term is 147, whose logarithm is 2.167317334748176. The logarithm must be base 10, because the published constants were fitted that way; a natural logarithm would shift every result by a constant multiple.

4. 4

   Build the denominator

   Multiply each logarithm by its coefficient and combine with the base constant. For the male case that is 1.0324 minus 0.19077 times 1.7160033436347992 plus 0.15456 times 2.255272505103306, which equals 1.0536129605235562. For the female case the corresponding denominator is 1.035557463772579. Keep every intermediate figure at full precision and round only at the very end.

5. 5

   Divide, subtract, then split the mass

   Dividing 495 by 1.0536129605235562 gives 469.811988411785478, and subtracting 450 leaves 19.811988411785478%. Applying that percentage to 80 kg gives 64.15040927057161 kg of lean mass and 15.849590729428385 kg of fat. The lean figure is the one most training and nutrition plans are actually trying to move, so report both rather than the percentage alone.