Body Fat Calculator
Estimate your body fat percentage with the U.S. Navy method.
This body fat calculator uses the U.S. Navy circumference method to estimate your body fat percentage from a few tape-measure measurements — no special equipment needed. Add your bodyweight and it also returns your fat mass, lean mass, and a fitness category.
Body fat percentage tells you something BMI can't: how much of your weight is fat versus muscle, bone, and water. Two people at the same BMI can have very different body compositions. All calculations happen in your browser, so your measurements stay on your device.
📖 Read the guide: How to Calculate Body Fat Percentage (3 Methods Compared)
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Formula
U.S. Navy — men
%BF = 495 ÷ (1.0324 − 0.19077·log₁₀(waist − neck) + 0.15456·log₁₀(height)) − 450
Uses neck and waist circumference plus height (all in centimetres). The difference between waist and neck stands in for abdominal fat.
U.S. Navy — women
%BF = 495 ÷ (1.29579 − 0.35004·log₁₀(waist + hip − neck) + 0.22100·log₁₀(height)) − 450
Adds the hip measurement, since women carry fat differently. All measurements are in centimetres; imperial inputs are converted automatically.
Body composition
fat mass = weight × %BF ÷ 100; lean mass = weight − fat mass
Once body fat percentage is known, your bodyweight splits into fat mass and everything else (lean mass) — muscle, bone, organs, and water.
How to use the body fat calculator
- 1Choose your sex and units. Measure with a flexible tape, snug but not compressing the skin.
- 2Neck: just below the larynx, sloping slightly down to the front. Waist: at the navel for men; at the narrowest point for women.
- 3Women also measure the hip at its widest point. Enter your height, and optionally your weight for fat and lean mass.
- 4Read your estimated body fat percentage and fitness category; measure first thing in the morning for consistency.
Examples
| Example | Input | Result |
|---|---|---|
| Male | 180cm, neck 40, waist 90 | ≈ 18.4% (Average) |
| Female | 165cm, neck 34, waist 75, hip 95 | ≈ 26.4% (Average) |
| With weight | 80 kg at 18.4% | Fat 14.7 kg · Lean 65.3 kg |
What is body fat percentage?
Body fat percentage is the share of your total bodyweight that is fat. The rest — muscle, bone, organs, and water — is your lean mass. It's a more meaningful health and fitness marker than scale weight alone, because it distinguishes a muscular 80 kg person from a less-fit one at the same weight. Some fat is essential: it cushions organs, stores energy, and supports hormones, which is why healthy ranges never reach zero.
Because women carry more essential fat (largely for reproductive health), healthy ranges are higher for women than men. That's also why the calculator asks for sex and, for women, the hip measurement — the same waist reading means something different depending on overall fat distribution.
How the U.S. Navy method works
The Navy method estimates body fat from body circumferences rather than skinfold calipers or a lab scan. It works because fat tends to accumulate in predictable places — around the waist for men, and the waist and hips for women — so the ratio of those measurements to height tracks overall fatness reasonably well across a population. The formula was developed by the Naval Health Research Center as a quick, equipment-light alternative to underwater weighing.
Its big advantages are convenience and repeatability: a tape measure costs little, and if you always measure the same way you'll capture changes over time accurately. Its limitation is that it estimates from shape, not direct measurement, so it's less precise than a DEXA scan or hydrostatic weighing — especially for very lean, very muscular, or very heavy bodies.
Body fat categories
The American Council on Exercise groups body fat into ranges that differ by sex. For men: essential fat is 2–5%, athletes 6–13%, fitness 14–17%, average 18–24%, and 25% or above is classed as obese. For women, who carry more essential fat: essential is 10–13%, athletes 14–20%, fitness 21–24%, average 25–31%, and 32% or above is classed as obese.
These bands are guides, not diagnoses. Athletes often sit at the lower end, while a healthy non-athlete may be comfortably in the average range. What usually matters more than a single reading is the direction of travel over months — and how you feel, perform, and recover.
This calculator provides a general estimate for educational use and is not medical advice or a substitute for clinical body-composition testing. Consult a healthcare professional for health or fitness decisions.
Frequently asked questions
How accurate is the U.S. Navy body fat calculator?
It's a good estimate — typically within a few percentage points of a DEXA scan for average builds — and excellent for tracking change over time if you measure consistently. It's less accurate for very lean, very muscular, or very heavy bodies. For a clinical figure, use DEXA or hydrostatic weighing.
How should I measure my waist and neck?
Use a flexible tape, snug but not digging in. Measure your neck just below the Adam's apple; measure your waist at the navel (men) or the narrowest point (women); women also measure the hip at its widest. Stand relaxed and don't suck in — measuring each morning improves consistency.
What's a healthy body fat percentage?
For men, the fitness range is roughly 14–17% and average is 18–24%; for women, fitness is about 21–24% and average 25–31%. Athletes are often lower. Ranges differ by sex because women carry more essential fat.
Body fat percentage or BMI — which should I use?
They answer different questions. BMI is a fast height-to-weight screen but can't tell fat from muscle. Body fat percentage estimates composition directly, so it's more useful for fitness goals. Many people track both — try our BMI Calculator alongside this one.
Does this calculator store my measurements?
No. All computation happens in your browser — nothing you enter is uploaded, logged, or stored on a server.
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