ProteinNavy Body Fat Calculator
The US Navy circumference method — a tape measure and three numbers. Works in inches or centimetres, reproduces official Navy scores exactly when you enable service rounding, and tells you how many inches you would need to lose to meet the standard.
Unrounded 16.5% · Fitness
- Age-graduated goal
- 23%
- Fat mass
- 29.7 lb
- Lean mass
- 150.3 lb
- Waist-to-height
- 0.485
The formula
Developed by Hodgdon and Beckett at the Naval Health Research Center in 1984, it predicts body density from circumference measurements and converts that to a fat percentage. All measurements are in inches and both logarithms are base 10 — using a natural logarithm instead is the single most common implementation bug and returns a negative body fat for a normal man.
MEN BF% = 86.010 × log₁₀(abdomen − neck) − 70.041 × log₁₀(height) + 36.76
WOMEN BF% = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387
↑ negativeWhere to measure
| Site | Where | Rounds |
|---|---|---|
| Neck (both) | Just below the larynx, tape sloping slightly down at the front. Never over the larynx. | Up to ½ in |
| Abdomen (men) | Across the navel, arms at sides, at the end of a normal relaxed exhale. | Down to ½ in |
| Natural waist (women) | Point of minimum circumference, roughly midway between navel and sternum — NOT the navel. | Down to ½ in |
| Hips (women) | Greatest protrusion of the glutes viewed from the side, tape parallel to the floor. | Down to ½ in |
| Height (both) | No shoes, head level. | Up to ½ in |
The neck rounding is a genuine trap: the Navy's own guide states in one place that all circumferences round down, then specifies in another that the neck rounds up. The specific instruction governs, and it is what reproduces official score tables.
Standards
The hard maximum is 26% for men and 36% for women, with no age banding. Exceeding it fails the body composition assessment. The graduated standards below are a lower bar: going over them does not fail the assessment but does mandate Fitness Enhancement Program enrolment.
| Age | Male | Female |
|---|---|---|
| 17–21 | 22% | 33% |
| 22–29 | 23% | 34% |
| 30–39 | 24% | 35% |
| 40+ | 26% | 36% |
How accurate is it?
Honestly: good for a tape measure, not a substitute for a scan. The men's equation came from 602 subjects with a correlation of 0.90 and a standard error around 3.5 percentage points. The women's came from 214 subjects at 0.85 and roughly 3.7 points, with cross-validation on a further 146 women giving standard errors of 4.0 to 4.4 points.
In practice that means a result of 20% is telling you the truth is probably somewhere between 16% and 24%. It is precise enough to track change over time on the same body with the same tape, which is what most people actually want, and too imprecise to treat a single reading as a fact about you.
Frequently asked questions
- What is the US Navy body fat formula?
- For men, body fat % = 86.010 × log₁₀(abdomen − neck) − 70.041 × log₁₀(height) + 36.76, with all measurements in inches. For women, 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387. Note that the women's final constant is negative. Both use base-10 logarithms, not natural logarithms.
- How accurate is the Navy body fat calculator?
- The men's equation was developed on 602 subjects with a correlation of 0.90 and a standard error of about 3.5 percentage points; the women's on 214 subjects at 0.85 and roughly 3.7 points. That means an individual result can reasonably sit three to four points either side of the true value. It estimates body fat well across a population and only approximately for any one person.
- Where exactly do I measure?
- Neck just below the larynx with the tape sloping slightly down at the front, for both sexes. Men measure the abdomen across the navel at the end of a relaxed exhale. Women measure the natural waist — the point of minimum circumference, which is above the navel, not at it — plus hips at the greatest protrusion of the glutes. Using the navel for a woman's waist is the most common measurement error.
- What are the Navy body fat standards?
- The hard maximum under OPNAVINST 6110.1K is 26% for men and 36% for women, with no age banding. Separate graduated standards under NAVADMIN 178/15 run from 22% to 26% for men and 33% to 36% for women by age band; exceeding those does not fail the physical fitness assessment but does mandate enrolment in the Fitness Enhancement Program.
- Does the Navy still use this method?
- Not for official assessments. The Navy has moved to a waist-to-height ratio screen, with a ratio at or below 0.5499 passing outright, and neck and hip are no longer measured at all. The circumference formula on this page remains what people mean by the Navy body fat calculator and is still a useful estimate, but it is no longer the operational test.
- Why does my result differ from another calculator?
- Usually rounding, or units. The Navy rounds the neck up to the nearest half inch and other circumferences down, which most calculators skip — the toggle above applies it. Separately, there are two published forms of this formula: a natively imperial linear equation and a metric body-density equation. They are different statistical fits, not conversions of each other, and can differ by up to about a percentage point. This calculator uses the imperial form, which is the one that reproduces official Navy tables exactly.
Unofficial tool. Not affiliated with the US Navy or Department of Defense. Only a measurement taken by your command counts for the record, and the Navy's current operational assessment is a waist-to-height screen rather than this circumference method.