Navy Body Fat Calculator
Estimate body fat percentage the way the U.S. Navy does — with a tape measure. Enter height, neck, and waist (plus hip for women) in inches or centimeters, and your weight (lb or kg) to see fat mass and lean mass too.
Example: with Sex Male · Units inches + pounds (US) · Height 70 · Neck circumference 15 · Waist at navel 34 → Body fat percentage: 17.5%.
- Category (ACE scale)Fitness (14-17.9%)
- Fat mass31.5 lb
- Lean mass148.5 lb
Computed by the calculator below using its default values. Change any input to see your own numbers.
U.S. Navy circumference method (Hodgdon & Beckett, 1984). Men use waist − neck; women use waist + hip − neck; log-based formulas in inches.
How the Navy measures body fat with a tape
The method comes from Hodgdon and Beckett's 1984 Naval Health Research Center study, which regressed circumference measurements against underwater weighing. The insight: neck size tracks lean tissue while waist (and hip, for women) tracks fat storage, so the gap between them — scaled logarithmically against height — predicts body fat surprisingly well. The military services still use versions of this for body-composition screening because it needs only a tape measure and a minute.
Measure at the right spots: waist horizontally at the navel (relaxed, not sucked in), neck just below the larynx, hips at the widest point. Against DEXA scans the estimate typically lands within about 3-4 percentage points — good for tracking trend, not for bragging rights to the decimal.
How it’s calculated
U.S. Navy circumference equations (inches): men %BF = 86.010×log10(waist − neck) − 70.041×log10(height) + 36.76; women %BF = 163.205×log10(waist + hip − neck) − 97.684×log10(height) − 78.387. Metric entries are converted at 1 in = 2.54 cm exactly. Fat mass = weight × %BF; lean mass = weight − fat mass. Categories follow the ACE body-fat scale.
Tape technique moves the answer a full point or more and the equation carries ±3-4% error versus lab methods, with extra bias at very high or low leanness — an educational estimate, not medical advice or an official military determination; for health decisions, get body composition assessed professionally.
ACE body fat categories
| Category | Women | Men |
|---|---|---|
| Essential fat | 10-13% | 2-5% |
| Athletes | 14-20% | 6-13% |
| Fitness | 21-24% | 14-17% |
| Average | 25-31% | 18-24% |
| Obese | 32%+ | 25%+ |
Source: American Council on Exercise (ACE) body fat percentage norms.
Common mistakes
- Measuring the waist at the narrowest point instead of at the navel — the Navy spec is at the navel, and it is usually bigger.
- Pulling the tape tight or flexing; it should be snug on relaxed skin, parallel to the floor.
- Forgetting the hip measurement applies only to the women's formula — it is ignored for men.
- Reading day-to-day changes as fat change; bloating and hydration move the waist by an inch.
Frequently asked questions
What formula does the Navy body fat calculator use?
The Hodgdon-Beckett (1984) equations. Men: %BF = 86.010×log10(waist − neck) − 70.041×log10(height) + 36.76; women: %BF = 163.205×log10(waist + hip − neck) − 97.684×log10(height) − 78.387, all in inches. A 5 ft 10 in man with a 34 in waist and 15 in neck comes out near 17.5%.
How accurate is the tape method versus a DEXA scan?
Studies put it within about 3-4 percentage points of lab methods for most people, with larger misses on very lean or very muscular builds (a thick neck reads as leanness). It shines at tracking your own trend with consistent technique.
Why does the women's formula include hips?
Women store proportionally more fat at the hips and thighs, so waist alone underestimates their fat mass. Adding the hip girth restores the correlation the regression needs.
Is this the same standard the military uses to pass or fail people?
It is the same measurement method, but each service sets its own allowable percentages by age and sex and has its own taping protocol and rounding rules. For an official determination, only your unit's measurement counts.
My result seems high (or low) — should I act on it?
Repeat the measurements on three mornings and average them before reacting. If body fat genuinely sits in the obese range, or you are considering an aggressive cut, loop in a physician or registered dietitian rather than dieting off one tape reading.