Body Fat Formula Explained

This reference explains the Body Fat formula used by our free Body Fat Calculator. Use it to understand variables, units, and common mistakes before you calculate.

The formula

Body fat % ≈ U.S. Navy circumference method from neck, waist, and hip measurements

Variables and units

• neck — Neck circumference below the larynx (cm or in)
• waist — Waist at navel level (cm or in)
• hip — Hip circumference (women only) (cm or in)

Worked example

Inputs: Male: waist 85 cm, neck 38 cm, height 178 cm

1. Apply U.S. Navy formula for men
2. BF% = 495 / (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450
3. log10(85 − 38) = log10(47) ≈ 1.672
4. log10(178) ≈ 2.250
5. BF% ≈ 495 / (1.0324 − 0.318 + 0.347) − 450 ≈ 18.2%

Result: Body fat ≈ 18% (fitness range for men)

When to use this formula

Use this formula when you need a quick body fat estimate with values you already know. Our Body Fat Calculator applies the same relationship automatically so you can verify handwritten work.

Common mistakes

• Measuring waist at the wrong point (should be at navel)
• Pulling tape too tight or leaving gaps
• Using hip measurement for men (women's formula only)

Frequently asked questions