Answer: Enter your values and the Body Fat Calculator returns the exact result instantly — formula, worked example, and a plain-English explanation are included below the tool.
Calculate your body fat percentage (US Navy Method)
This tool uses the U.S. Navy circumference method: you enter height and neck and waist measurements (plus hip for women), and it applies the Navy's published regression equations to estimate body fat percentage. The method was developed from anthropometric data on Navy personnel and remains a standard field technique because it needs nothing but a tape measure. Enter your measurements in the form above and the estimate appears instantly — all math runs locally in your browser.
Measurement technique drives accuracy. The Navy protocol measures the neck just below the larynx, the waist at the navel for men (at the point of minimal circumference for women), relaxed, not sucked in, with the tape snug but not compressing skin. Repeat each measurement three times and average; a centimeter of sloppiness moves the estimate noticeably.
Every field method estimates rather than measures directly, and each carries its own error band. The table below places the Navy method among the common alternatives.
| Method | Inputs needed | Sex-specific | Notes |
|---|---|---|---|
| U.S. Navy circumference (this tool) | Height, neck, waist (+ hip for women) | Yes | Estimates only; tape-measure precision matters |
| BMI | Height, weight | No | Screens weight categories, not body composition |
| Skinfold calipers (Jackson-Pollock 3-site) | 3 skinfold measurements | Slightly (site choice) | Practical field method, ~3-4% typical error |
| Bioelectrical impedance (BIA) | Scale or handheld device | Yes | Sensitive to hydration and recent meals |
| DXA scan | Full-body X-ray scan | No | Common research reference standard |
| Hydrostatic weighing | Underwater immersion | No | Traditional gold standard, impractical daily |
Even reference methods disagree with each other by a few percentage points, so treat any single number as an estimate and track the trend under consistent conditions instead of comparing readings taken by different methods.
The American Council on Exercise publishes the fitness-category bands most gyms and apps use. They're descriptive population bands for adults, not medical 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%+ |
Essential fat — the minimum needed for basic physiology — is commonly cited around 2-5% for men and 10-13% for women, and staying at the extreme low end is neither healthy nor sustainable for most people. Women's bands sit about seven points higher across the board because sex-specific fat, concentrated around the hips and thighs, is wired into reproductive hormone production. For the full story behind these bands, see what a healthy body fat percentage is.
Body fat percentage matters because weight alone conflates fat and lean mass. Two people at the same height and weight can carry very different compositions, with different health implications; body mass index (BMI) cannot see that difference, which is its best-known limitation as a screening tool.
Run the calculator's default male input through the equation: height 175 cm, neck 38 cm, waist 85 cm. Waist minus neck is 47 cm, the log terms feed the Navy regression, and the result is 16.9% — squarely in the fitness band. At a body weight of 80 kg, that reading splits into 13.6 kg of fat mass and 66.4 kg of lean mass, the two numbers any body-composition goal is really about.
The female equation adds a hip measurement. At 165 cm with a 34 cm neck, 74 cm waist, and 95 cm hips, the estimate comes out at 25.9%, the middle of the average band. The hip term does real work: the women's regression accounts for fat distributed around the hips and thighs, which the male equation would misread badly.
Healthy change is slow: a realistic pace for fat loss with resistance training preserved is commonly described as losing about 0.5-1% of body weight per week, part of which may be lean mass without training and adequate protein. Re-measure under the same conditions — same time of day, same hydration, same tape placement — because water shifts alone can move a circumference-based estimate. The Navy method's typical error is on the order of three percentage points versus densitometry, so single readings matter less than the direction of repeated readings taken the same way.
This tool is an estimator, not a diagnostic device. For medical decisions, body-composition questions belong with a clinician who can order appropriate testing.
Consistency beats precision. Measure in the morning, before food and drink shift your waistline. Use a flexible tape, keep it level and horizontal, and have a second person measure your neck if possible. For the neck, measure just below the larynx with shoulders relaxed; for men's waist, at the navel; for women's waist, at the natural narrowest point; for the hip, at the fullest point of the buttocks. Take each measurement at the end of a normal exhale, and repeat three times, averaging the closest two if one lands far off.
Record everything to the nearest quarter inch or half centimeter and enter the same unit consistently in the form — mixing units is the most common input error. Because the equations are regressions fit to a specific population sample, they are least reliable at body shapes far from that sample, which is one reason very lean athletes and people with high muscle mass see less accurate estimates from any circumference formula.
Finally, interpret trends rather than single points: if three successive readings taken the same way show a downward drift, the drift is real; a single low reading after a big dinner is not. Body composition changes on the scale of months, not days, and the tape measure rewards patience more than frequency.
The category bands above don't move with birthdays, but population averages drift up with age, mostly because lean mass quietly leaves unless you train against it. National survey DXA data puts the typical American man in the high 20s and the typical woman around 40% — well above the middle of the ACE average band, and a reminder that "average" and "healthy" overlap without being identical.
Progress is also slower than the fitness industry implies. An 80 kg man at 17% body fat who loses half a kilo of fat a week while holding lean mass moves his percentage by only about half a point in the first week, and the pace tightens as he leans out. That's why a visible transformation is a twelve-week project: the number is honest, it's just not fast. A moderate calorie deficit, enough protein, and resistance training do the moving; the tape measure every few weeks keeps score.
How accurate is the Navy method? Expect roughly ±3 percentage points versus lab reference methods when measurements are taken carefully; error grows with careless tape placement.
Why do women need a hip measurement? The Navy equation for women includes hip circumference because fat distribution differs by sex; men's equations use only neck and waist.
What's a healthy body fat percentage? ACE's commonly cited average bands run 18-24% for men and 25-31% for women; athletes sit lower. Individual targets should account for age, sport, and health status.
Can I use this if I'm very muscular? Circumference methods overestimate fat in people with large neck or waist musculature, since the equations assume typical lean-to-fat ratios.
How often should I remeasure? Every few weeks under identical conditions is plenty; daily readings mostly track hydration and tape placement noise.
What's the difference between essential fat and storage fat? Essential fat is the minimum for basic physiology, commonly cited as 2-5% for men and 10-13% for women. Everything above it is storage fat the body draws on for energy; women's higher floor reflects sex-specific deposits tied to reproductive function.
Does body fat percentage change with age? The published bands don't shift, but population averages drift up as untrained lean mass declines. Strength training and protein change what the tape says at any age.