How to measure
- Neck: just below the larynx, with the tape sloping very slightly downward at the front.
- Waist: men measure at the navel; women at the narrowest point.
- Hip (women): at the widest point of the buttocks.
Measurement error is the largest single source of error in this method — a centimetre at the waist can move the result by more than a percentage point, so take each measurement twice and use the average.
The formula behind the result
The Navy method applies a logarithmic formula to your circumference measurements, with all values in inches:
- Men: 495 ÷ (1.0324 − 0.19077×log₁₀(waist−neck) + 0.15456×log₁₀(height)) − 450
- Women: 495 ÷ (1.29579 − 0.35004×log₁₀(waist+hip−neck) + 0.221×log₁₀(height)) − 450
Worked example: a man with a 34″ waist, 15″ neck and 70″ height. Waist minus neck is 19, so the calculation is 495 ÷ (1.0324 − 0.19077×log₁₀(19) + 0.15456×log₁₀(70)) − 450 ≈ 11.1%, which lands in the athlete band on the scale above.
Where this method comes from
The equations were developed at the US Navy's Naval Health Research Center by Hodgdon and Beckett in 1984, and validated against hydrostatic (underwater) weighing — the reference standard for body composition at the time — in active-duty personnel. They remain in use for military body-composition screening, which is a reasonable endorsement of their practicality if not their precision.
That origin also explains a limitation: the sample was military personnel, who are fitter and more narrowly distributed in age and body type than the general population. The formula performs best on bodies resembling that sample.
Healthy body-fat ranges
- Women: Essential 10–13% · Athletes 14–20% · Fitness 21–24% · Average 25–31% · Higher 32%+
- Men: Essential 2–5% · Athletes 6–13% · Fitness 14–17% · Average 18–24% · Higher 25%+
The gap between the sexes is physiological, not a scoring adjustment: women carry substantially more essential fat as a structural part of hormonal, neurological and reproductive function. A woman at 22% is athletic; a man at 22% is average. Read your number against your own column, and see the body fat chart for the full breakdown.
How accurate is the US Navy method?
Accurate enough to track your own trend, not accurate enough to argue about a single reading. Circumference equations of this family typically land within about three to four percentage points of a DXA scan for most adults, with the error widening at the extremes of leanness and body size.
That sounds worse than it is until you see what the alternatives manage. A 2010 comparison of field methods against DXA in college-aged adults found consumer skinfold calipers had a total error of 7.9 to 10.9 percentage points — worse than a tape measure. Even the better digital caliper managed 95% limits of agreement of only ±6.4 points in men and ±4.9 in women, and the self-administered model was worse again at ±8.6 and ±7.5.
The approach is also still actively researched rather than a 1980s relic. The US Army revalidated its circumference equations against DXA in 1,904 active-duty soldiers in 2024, and a 2025 follow-up compared three-site and one-site equations alongside bioelectrical impedance in the same cohort. That work found dropping from three measurement sites to one had minimal impact on accuracy — a useful reminder that more measurements do not automatically mean a better estimate, and that how you measure matters more than how many places you measure.
How the home methods compare
Nothing you can do at home measures body fat. Every option estimates it, so the honest comparison is how large the error is, what it costs, and whether you can repeat it identically month after month. People consistently underrate that last column: a method with a wider error that you repeat the same way every time will show you a real trend, while a more accurate method used inconsistently will not.
| Method | Typical error vs DXA | Cost | Best for |
|---|---|---|---|
| US Navy tape | ~3–4 percentage points | Free | Tracking your own trend at home |
| DXA scan | The reference standard | Paid, per scan | One accurate baseline |
| Skinfold calipers | 7.9–10.9 points (consumer models) | Low | Trained assessors only |
| Bioelectrical impedance | Varies widely with hydration | Low to moderate | Convenience; poor absolute accuracy |
| Hydrostatic weighing | Close to DXA | Rarely available | Research settings |
Caliper figures are measured values from the 2010 validation study cited below. The tape and impedance figures are typical ranges reported across validation studies rather than single measurements. Every method here is an estimate.
Why body fat beats the scale
Two people at identical height and weight can look and function entirely differently depending on how much of that weight is muscle. Body-fat percentage is what separates them.
It also explains the stalled scale. If you are training consistently with enough protein, it is common to lose fat and gain muscle at similar rates for a while. The scale barely moves, which reads as failure and causes a lot of people to abandon a programme that is working. A tape measure would have shown the progress.
Changing it sensibly
Losing fat at roughly 0.5–1% of body weight per week, with adequate protein and regular resistance training, preserves far more muscle than an aggressive deficit. That matters for the outcome you actually want: a higher final muscle mass is what makes any given body-fat percentage look and perform the way people imagine it will. Going below the essential range is not an achievement but a medical state, and for women it is associated with disrupted menstruation and reduced bone density.