How to measure yourself
- Use a soft tape measure held flat against the skin, snug but not pressing in.
- Neck: just below the Adam's apple, with the tape level all the way round.
- Waist: men at the navel; women at the narrowest point. Breathe out normally first.
- Hips (women): around the widest part of the buttocks.
- Measure two or three times and use the average, then enter your height and measurements.
The US Navy formula
With all measurements in inches:
- Men:
body fat % = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76 - Women:
body fat % = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387
Hodgdon and Beckett developed these equations for the US Navy in 1984, and the US military used them from 2002 until it adopted a new method in 2023. Metric measurements are converted to inches first (1 inch = 2.54 cm).
Worked example
A man 70 inches (177.8 cm) tall with a 16-inch neck and a 34-inch waist:
- waist − neck = 18, and log10(18) ≈ 1.2553; log10(70) ≈ 1.8451.
- 86.010 × 1.2553 − 70.041 × 1.8451 + 36.76 ≈ 107.97 − 129.23 + 36.76 = 15.5%.
- On ACE's chart that's in the fitness range for men (14–17%).
Body fat categories
The American Council on Exercise's norms:
| Category | Women | Men |
|---|---|---|
| Essential fat | 10–13% | 2–5% |
| Athletes | 14–20% | 6–13% |
| Fitness | 21–24% | 14–17% |
| Acceptable | 25–31% | 18–24% |
| Obesity | 32% and over | 25% and over |
ACE gives whole-number ranges, so a result such as 20.5% is placed in the lower band.
How accurate is it?
It's an estimate. In a 2023 study of army recruits the tape method read about 6 percentage points below a DXA scan on average, and the equations are known to underestimate high body fat and overestimate low body fat. Small measuring errors matter too: a waist measured 2 cm out moves the result by a point or more. Use the same tape, time of day and technique each time, and watch the trend rather than one reading.
Not medical advice
This is an estimate of body composition, not a diagnosis. It isn't suitable during pregnancy. If you're concerned about your weight or body fat, talk to a doctor.
Sources
Each link was last checked on .
- US Army Accession and Retention Standards: Impact on Obesity and Medical Readiness, Military Medicine (Potter and Friedl) (2025): the Hodgdon and Beckett (US Navy, 1984) equations, used by the US military from 2002 until 2023.
- Body composition changes during 8 weeks of military training are not accurately captured by circumference-based assessments, Frontiers in Physiology (Foulis et al.) (2023): the equations in centimetres, and that they read about 6 points lower than a DXA scan on average.
- Percent body fat norms for men and women, American Council on Exercise (archived copy) (2022): the essential fat, athletes, fitness, acceptable and obesity ranges.
Common uses
- Tracking a fitness programme. Measure every few weeks with the same tape and technique to see whether your body fat is moving, which the scale alone can hide.
- When BMI seems wrong. If muscle puts your BMI in the overweight range, an estimate of body fat gives a second view of your body composition.
- Without special equipment. All you need is a tape measure: no callipers, smart scale or lab scan.