Calculators

Body Fat Calculator

Estimate your body fat percentage from a tape measure, using the US Navy circumference method.

How it works

The Navy formula estimates body density from how your waist compares with your neck and height, then converts density to fat percentage with the Siri equation. Women's bodies store fat differently, so their version adds the hip: 495 ÷ (1.29579 − 0.35004 log(waist + hip − neck) + 0.22100 log(height)) − 450. All measurements are in centimetres.

men: 495 ÷ (1.0324 − 0.19077 log(waist − neck) + 0.15456 log(height)) − 450
Neck
Just below the larynx
Waist
At the navel for men, the narrowest point for women
Hip
Widest point of the buttocks (women only)
log
Base-10 logarithm

Worked example

A man 178 cm tall weighing 80 kg, with a 38 cm neck and an 86 cm waist.

  1. 1Waist − neck = 48; log(48) = 1.6812
  2. 2log(178) = 2.2504
  3. 3Density term: 1.0324 − 0.19077 × 1.6812 + 0.15456 × 2.2504 = 1.0595
  4. 4495 ÷ 1.0595 − 450 = 17.2%

About 17.2% body fat, in the fitness range: 13.8 kg of fat and 66.2 kg of lean mass.

Frequently asked questions

What is a healthy body fat percentage?

The American Council on Exercise puts average at 18–24% for men and 25–31% for women, with fitness levels at 14–17% and 21–24%. Women carry more essential fat, so their ranges sit higher. Above 25% for men or 32% for women is classed as obese.

How accurate is the Navy method?

For most people it lands within 3–4 percentage points of DEXA, the clinical reference. Accuracy depends on measuring carefully: tape snug but not compressing, at the same spots, relaxed. It is better at tracking change over time than at giving an exact figure.

Is body fat percentage better than BMI?

It says more, because it separates fat from muscle. A muscular person can have a BMI in the overweight range with healthy body fat. BMI is easier to measure and is what most health guidelines use, so the two work well together.

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