How to Calculate Body Fat Percentage

Formula

Men: density = 1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)

Women: density = 1.29579 − 0.35004 × log10(waist + hip − neck) + 0.221 × log10(height)

body fat (%) = 495 / density − 450

• height: your height without shoes, in centimetres
• neck: neck circumference just below the larynx, in centimetres
• waist: waist circumference, at the navel for men and at the narrowest point for women, in centimetres
• hip: hip circumference at the widest point, in centimetres; in the equation for women only
• log10: the base-10 logarithm
• density: the estimated body density. The second operation is the Siri equation; it turns density into percent fat.

Hodgdon and Beckett published the equations in 1984 for U.S. Navy personnel. Body fat is rounded to 0.1.

Step-by-step example

A man of 80 kg and 178 cm with a 90 cm waist and a 38 cm neck:

1. Girth: 90 − 38 = 52 cm.
2. Body density: 1.0324 − 0.19077 × log10(52) + 0.15456 × log10(178) = 1.05286.
3. Body fat: 495 / 1.05286 − 450 = 20.1%.
4. Fat mass: 80 × 20.1% = 16.1 kg.
5. Lean body mass: 80 − 16.1 = 63.9 kg.
6. Class: 20.1% is in the average class (18–24%) for men in the ACE table.

An example for a woman: 60 kg, 165 cm, neck 32 cm, waist 72 cm, hip 96 cm. The girth is 72 + 96 − 32 = 136 cm, the density 1.03903, the body fat 26.4% and the fat mass 15.8 kg.

How to read the result

The American Council on Exercise (ACE) table puts body fat into five classes:

Essential fat is the lowest level the body needs to work. The limits for women are higher.

How much does the measurement change the result?

The waist changes the result most. For the same man (178 cm, neck 38 cm, 80 kg), when only the waist changes:

So put the tape at the same place each time, level and not tight, and do not pull your stomach in. The method is an estimate; it can differ by about 3–4 points from underwater weighing or a DEXA scan. The change between measurements taken in the same conditions tells you more than one measurement.