Body fat from a tape measure
The US Navy method (the Hodgdon–Beckett formula) estimates body fat from body circumferences instead of a scale. Men use neck and waist; women add hips. Measure the waist at the navel and the neck just below the larynx, on an empty stomach, with the tape snug but not compressing. It is free, takes about two minutes, and only breaks down at the extremes of build.
The circumference formula
All measurements in centimeters; log is base 10. The waist-minus-neck term is what the estimate really tracks.
Because the estimate rides on waist minus neck, a bigger waist relative to the neck reads as more fat. As a rough gut check for men, a waist more than about 25 cm larger than the neck usually means body fat above 20%.
Healthy ranges and thresholds
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Obese | 25%+ | 32%+ |
Bands are the American Council on Exercise classification. Women need more essential fat than men for hormonal and reproductive function, so a woman's 20% is athletically comparable to roughly 12% in a man. Visible abs usually need about 10–14% for men and 16–20% for women.
Getting a reliable reading
- Measure the same way each time. The waist can swell 2–5 cm after a meal, so take it in the morning, fasted, and keep the conditions constant.
- Don't mix methods. Navy and caliper estimates on the same person can differ by 3–5 points. Track the trend with one method rather than comparing tools.
- The number is an estimate. It is a screen, not a diagnosis, and the direction of change over 8–12 weeks matters more than any single figure.
Common questions
What measurements does the Navy body fat method need?
A tape measure and your height. Men measure neck and waist; women measure neck, waist and hips. No scale, calipers or lab equipment are required.
How accurate is the Navy tape method?
It lands within about 3 to 4 percent of hydrostatic weighing for average builds. It can overstate body fat on very muscular people and understate it when fat is carried internally, but it is accurate enough that the US military uses it officially.
What is a healthy body fat percentage?
Roughly 14 to 24 percent for men and 21 to 31 percent for women. The fitness band is about 14 to 17 percent for men and 21 to 24 percent for women. Dropping below essential fat, under 2 to 5 percent for men or 10 to 13 percent for women, is unsafe.
