Body Fat Calculator (US Navy Method)
How much of your weight is fat, and how much is lean tissue?
- Based on standard published formulas
- Instant, easy-to-read estimates
- Private: nothing leaves your device
Body Fat Calculator (US Navy Method)
Enter your numbers and press Calculate
How to take your measurements
The calculator walks you through each field like a short wizard. The formula does the math — your job is taking four honest measurements:
1. Sex. Toggle the switch. The male formula uses neck and waist; the female formula adds the hip measurement. 2. Height. In centimeters, barefoot, standing tall. If you know your height in feet and inches, multiply total inches by 2.54 — for example, 5'10" is 70 in × 2.54 = 178 cm. 3. Neck. Wrap the tape just below the larynx (Adam's apple), sloping slightly downward at the front. Snug, not tight. 4. Waist. For men, at navel level; for women, at the narrowest point of the torso. Measure at the end of a normal exhale — no sucking in. 5. Hip (women only). Around the widest part of the glutes, feet together. A 38-inch hip is 96.5 cm. 6. Weight. In kilograms (pounds ÷ 2.2046). It splits your percentage into fat mass and lean mass in kilos.
Use a soft sewing tape, not a stiff carpenter's tape, and take each measurement twice. If the two readings differ by more than half an inch, measure a third time and average them.
The US Navy formula, step by step
The method was developed in 1984 by Hodgdon and Beckett at the Naval Health Research Center. It uses base-10 logarithms (log10) of body circumferences, with every measurement in centimeters:
Men: body fat % = 495 / (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450
Women: body fat % = 495 / (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450
The calculator then splits your weight into two components:
fat mass = weight × body fat % / 100 · lean mass = weight − fat mass
Worked example. A 5'10" (178 cm) man with a 16.1" neck (41 cm), a 40.9" waist (104 cm), weighing 216 lb (98 kg):
1. waist − neck = 104 − 41 = 63 cm 2. log10(63) = 1.7993 and log10(178) = 2.2504 3. Denominator: 1.0324 − 0.19077 × 1.7993 + 0.15456 × 2.2504 = 1.0370 4. 495 / 1.0370 = 477.4 → 477.4 − 450 = 27.4% body fat 5. Fat mass: 98 × 0.274 = 26.8 kg (about 59 lb) · Lean mass: 98 − 26.8 = 71.2 kg (about 157 lb)
At 27.4%, this man falls in the obese range of the American Council on Exercise classification (25%+ for men). The output is clamped to 0-75% so that a badly mistyped measurement can't produce an impossible figure.
Common mistakes and method limits
The most common source of error isn't the formula — it's the tape. With the example man's numbers (5'10"), a single extra centimeter on the waist (less than half an inch) pushes the result up by almost a full percentage point. Typical mistakes:
- Tape too loose or too tight. It should touch the skin without compressing it. If it leaves a mark, it's too tight; if you can slide two fingers under it easily, it's too loose.
- Tape not level. At the waist and hip it must stay parallel to the floor all the way around. Measuring in front of a mirror helps a lot.
- Sucking in, or measuring after a big meal. Measure at the end of a normal exhale, ideally in the morning before breakfast; post-meal bloating can add an inch.
- Neck measured over the Adam's apple. The correct spot is just below the larynx; measuring above it inflates the circumference and artificially lowers the result for men.
Method limits: against a DEXA scan, the typical error is ±3-4 percentage points. It tends to underestimate body fat in very muscular people with thick necks, and accuracy drops at very low (under 8%) or very high percentages. It is not validated for minors or during pregnancy. If you enter a waist smaller than or equal to the neck, the result is pinned at 0% — double-check your measurements.
Worked examples
Three profiles run through the US Navy formula (measurements in cm, weight in kg):
| Profile | Height | Neck | Waist | Hip | Weight | Body fat | Fat mass | Lean mass |
|---|---|---|---|---|---|---|---|---|
| Tall man, 6'3" | 190 | 42 | 100 | — | 105 (231 lb) | 22.2% | 23.4 kg | 81.6 kg |
| Woman, 5'6" | 168 | 33 | 68 | 92 | 56 (123 lb) | 20.9% | 11.7 kg | 44.3 kg |
| Man, 5'8" | 172 | 37 | 90 | — | 78 (172 lb) | 21.9% | 17.1 kg | 60.9 kg |
Notice how the 6'3" man and the 5'8" man land on nearly the same percentage (22.2% vs 21.9%) despite a 27-kilogram weight gap: what drives the result is the waist-to-neck relationship relative to height, not the scale weight. The woman at 20.9% sits in the ACE fitness range for women (21-24%), close to the athletic band.
Disclaimer: this calculator is provided for educational and informational purposes only. It is not medical advice and does not replace an assessment by a physician or a registered dietitian.
About this calculator
A bathroom scale alone can't answer that: two people who both weigh 180 pounds can carry completely different body compositions. This calculator estimates your body fat percentage using the US Navy circumference method, developed at the Naval Health Research Center in San Diego — the same assessment the Navy has used since the 1980s for its fitness standards. You only need a soft tape measure: neck, waist and, for women, hips. Enter your measurements in centimeters (1 inch = 2.54 cm) and you'll get your body fat percentage plus your fat mass and lean mass in kilograms — useful numbers whether you're cutting, bulking or simply tracking progress month to month. Keep in mind this is an educational estimate, not a clinical diagnosis.
Frequently asked questions
How accurate is the US Navy method compared with a DEXA scan?
In the original validation studies (Hodgdon and Beckett, 1984) and later comparisons, the US Navy method shows a typical error of ±3-4 percentage points against reference methods such as DEXA or hydrostatic weighing. It is less precise than those lab tests, but more stable than many consumer bioimpedance scales, whose readings swing with hydration. Its real strength is repeatability: measure under the same conditions each time and the trend over the weeks becomes genuinely informative.
What body fat percentage is considered healthy?
According to the American Council on Exercise (ACE) classification, for men: essential fat 2-5%, athletes 6-13%, fitness 14-17%, acceptable 18-24% and obesity from 25%. For women: essential 10-13%, athletes 14-20%, fitness 21-24%, acceptable 25-31% and obesity from 32%. Women carry more essential fat for hormonal and reproductive reasons. These bands are guidelines that shift with age; a healthcare professional can evaluate your individual situation.
Why is the hip only measured for women?
Because fat distribution differs by sex: men tend to store fat around the abdomen (android pattern) while women store it on the hips and thighs (gynoid pattern). When the Navy researchers built the equations, they found that for men the waist-minus-neck difference already explained body fat well, whereas for women adding the hip circumference clearly improved accuracy. If you select male, the hip field is simply ignored in the calculation.
How is this different from BMI?
BMI only relates weight to height: it can't tell whether those pounds are muscle or fat, which is why a bodybuilder can read as overweight while carrying 10% body fat. The US Navy method estimates the fat percentage directly from body circumferences, so it separates fat mass from lean mass. The sensible approach is using both as complementary indicators — and for any health concern, seeing a professional: this tool is not a substitute for medical advice.