How to use
- Use a non-stretch tape, kept level and snug but not tight.
- Measure your neck just below the Adam’s apple.
- Measure your waist. Men: across the navel. Women: at the narrowest point.
- Women only: measure your hips at the widest part of the buttocks.
- Enter your height and measurements. Measure twice and use the average.
Formula
This is the US Navy circumference method (Hodgdon and Beckett, 1984), in the inch form behind the Navy’s official tables:
Men: %BF = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76
Women: %BF = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387
All measurements are in inches. Centimetres are divided by 2.54 first, so both units give the same answer.
Examples
- Man, 178 cm, neck 38 cm, waist 86 cm: 17.3%, in ACE’s “Fitness” band.
- Woman, 165 cm, neck 33 cm, waist 72 cm, hips 98 cm: 27.2%, in the “Average” band.
Body fat categories (ACE)
| Category | Women | Men |
|---|---|---|
| Essential fat | 10–13% | 2–5% |
| Athletes | 14–20% | 6–13% |
| Fitness | 21–24% | 14–17% |
| Average | 25–31% | 18–24% |
| Obese | 32% or more | 25% or more |
Limits of the tape method
- The typical error is about 3.5 percentage points against underwater weighing.
- It tends to read low at high body fat.
- It was built on US Navy personnel, so it is less certain for older or very muscular people.
- It is not valid in pregnancy or for children.
The 1984 metric version and military changes
Some calculators use the original 1984 metric (body density) equations. For the man above they give 17.2% instead of 17.3%. The two versions usually differ by under half a point.
Since January 2026 the US military screens first with waist-to-height ratio (below 0.55). Tape-based body fat is now a follow-up step, so this page is not an official military test.
For a quick screening number from height and weight alone, try the BMI calculator.