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What is Body Fat Calculator?

Free body fat percentage calculator. Uses 3 methods side-by-side: the US Navy formula, a BMI-based estimate, and a skinfold-based estimate — with confidence ranges for each. No signup.

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Body Fat Calculator runs entirely in your browser using JavaScript (browser). Your data never leaves your device.

Free Body Fat Calculator

Get three independent body fat estimates and understand where they agree. The US Navy method uses circumference measurements (neck, waist, hip for women) and is the most accessible without equipment. The BMI-based estimate derives body fat from your BMI, sex, and age. The skinfold estimate explains what caliper measurements would add. See all three side-by-side with confidence ranges so you understand the uncertainty in each method.

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Circumference measurements (Navy method)

cm
cm

Measure neck below the larynx. Waist at navel (men) or narrowest point (women). Hip at widest point (women only). Tape parallel to floor, measured at end of exhale.

Navy method

23.0%

Average

±3–4%

BMI-based

21.0%

Average

±4–6%

Skinfold (est)

21.5%

Average

±3% (with calipers)

Lean mass (Navy est.)

61.6 kg

Fat mass (Navy est.)

18.4 kg

Body fat categories (men)

Essential fat2–6%
Athletic6–14%
Fitness14–18%
Average18–25%
Obese25–40+%

Improve your body composition

Check your Fitness Age or get structured training from RowGress workouts. More free fitness calculators →

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Frequently Asked Questions

The US Navy circumference method estimates body fat using neck, waist, and (for women) hip measurements. For men: %BF = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76. For women: %BF = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387. It typically estimates within ±3–4% of DEXA scan results.
DEXA (dual-energy X-ray absorptiometry) and hydrostatic weighing are the gold standards but require specialized equipment. Among field methods, the Navy circumference method is practical and reasonably accurate (±3–4%). Skinfold calipers with a trained technician are also reliable (±3%). BMI-based estimates are least accurate at the individual level but require no measurements beyond weight and height. No formula replaces a direct measurement.
For men: essential fat = 2–5%, athletes = 6–13%, fitness = 14–17%, average = 18–24%, obese ≥ 25%. For women: essential fat = 10–13%, athletes = 14–20%, fitness = 21–24%, average = 25–31%, obese ≥ 32%. These ranges are guidelines — optimal body fat varies by age, genetics, and health goals.
BMI is a height-to-weight ratio that does not directly measure fat. Body fat percentage measures what fraction of your total body mass is fat tissue. Two people with identical BMIs can have very different body fat percentages depending on their muscle mass, bone density, and fat distribution. Body fat percentage is a more direct measure of body composition.
Measure at the end of a normal exhale (not held breath). Neck: measure below the larynx (Adam's apple), slightly downward slope. Waist (men): at the navel. Waist (women): at the narrowest point, usually 1 inch above the navel. Hip (women): at the widest point of the hips and buttocks. Use a soft measuring tape, keep it parallel to the floor, and take 2–3 measurements to confirm consistency.

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Body Fat Methods Compared

No field method measures body fat directly — they all estimate it by measuring a proxy (circumferences, BMI, or skinfold thicknesses) and applying a formula derived from populations where the proxy was correlated against a reference method (usually DEXA or hydrostatic weighing). The accuracy of any formula depends on how well you match the population it was calibrated on.

US Navy Circumference Method

Developed by Hodgdon and Beckett (1984) for the US military, this method uses neck, waist, and (for women) hip circumferences. It is the most practical field method — all you need is a soft tape measure. Typical error is ±3–4 percentage points versus DEXA. It tends to overestimate body fat in very muscular individuals with large waist measurements relative to their leanness.

BMI-Based Estimate (Deurenberg)

The Deurenberg formula (1991) predicts body fat from BMI, age, and sex: %BF = (1.20 × BMI) + (0.23 × age) − (10.8 × sex) − 5.4, where sex = 1 for male and 0 for female. This is convenient but less accurate for athletes and older adults. Typical error is ±4–6%. Use it as a cross-check, not a primary measure.

Skinfold Calipers

The Jackson-Pollock 3-site and 7-site skinfold protocols, performed by a trained technician with proper calipers, achieve ±3% accuracy. Without a technician and quality calipers, error increases substantially. Skinfold measurement is included in this tool as an explanatory method with estimated ranges, not an interactive input — because without knowing your actual skinfold thicknesses, any skinfold-based number would be meaningless.

Improve Your Composition With Training

Body fat percentage changes primarily through resistance training and calorie management. For structured programming, try RowGress workouts or check your Fitness Age to see how your body composition compares to others your age. Explore all free fitness calculators on RowGress for macro planning, calorie targets, and more.