The formula depends on waist minus neck
The Navy (Hodgdon-Beckett) method feeds your tape measurements, in inches, into a log-based equation. Men use waist minus neck; women add hip circumference to the waist term.
W = waist, N = neck, P = hip, H = height, all in inches; log is base 10.
How to tape yourself
A loose or badly placed tape is the biggest source of error. Stand relaxed and upright, keep the tape level, and use light tension so it sits on the skin without squeezing.
- Neck. Just below the larynx (Adam's apple), tape sloping slightly down at the front. Do not flex.
- Waist (men). Around the navel, horizontal. Breathe normally and do not pull the stomach in — sucking in falsely lowers the result.
- Waist (women). At the narrowest point, usually midway between the lowest rib and the navel.
- Hip (women only). Around the widest part of the buttocks, tape level with the floor.
- Repeat and average. Take each measurement two or three times and average; even a 1-inch height error shifts the result by roughly half a percent.
What the percentage means
| Category | Men | Women |
|---|---|---|
| Essential fat | 3–5% | 9–11% |
| Athletic | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Obese | 30%+ | 37%+ |
Navy pass limits are looser and rise with age: for men, 22% at 18–21 up to 26% at 40+; for women, 33% at 18–21 up to 36% at 40+.
Where it beats a bathroom scale
- It reads muscle, BMI doesn't. A muscular 200 lb, 5'10" man scores as "overweight" on BMI but lands near 15% (athletic) here, because the neck measurement credits lean mass.
- Consistency matters more than the exact number. Measured the same way every 4 to 8 weeks, the trend is reliable even if the absolute figure is a few points off.
- Not for everyone. It over-reads very lean athletes, under-reads high body fat, and is not valid during pregnancy.
Common questions
Which measurements does the Navy method need?
Height, neck and waist for men; height, neck, waist and hip for women. All are taken with a soft tape in inches. No scale is involved, since it estimates body fat from circumference, not weight.
How accurate is the Navy tape method?
Within about 3 to 4 percent of hydrostatic (underwater) weighing for people in the normal range. It tends to overestimate very lean athletes and underestimate people above about 30 percent body fat.
Why does neck size lower the result?
Neck circumference stands in for lean muscle and bone, which barely changes with weight. Subtracting it from the waist isolates the fat carried around the midsection, so a thicker neck signals more muscle and a lower fat estimate.
