Body Fat Calculator
Estimate body fat percentage using the U.S. Navy circumference method.
About the Body Fat Calculator
Body fat percentage gives a more direct picture of body composition than weight or BMI alone, distinguishing lean mass from fat mass. This calculator uses the U.S. Navy circumference method, a tape-measure-based formula that is widely used because it requires no special equipment.
How It Works
The Navy method uses the logarithm of waist and neck circumference (plus hip circumference for women) relative to height to estimate body fat percentage — a statistically derived formula validated against more expensive body composition measurement methods.
Men: %BF = 495/(1.0324 − 0.19077×log₁₀(waist−neck) + 0.15456×log₁₀(height)) − 450. Women: %BF = 495/(1.29579 − 0.35004×log₁₀(waist+hip−neck) + 0.22100×log₁₀(height)) − 450.
Worked example
Scenario: A man 178 cm tall with an 86 cm waist and a 38 cm neck.
- Waist minus neck: 86 − 38 = 48 cm.
- Navy formula (men): 495 ÷ (1.0324 − 0.19077 × log10(48) + 0.15456 × log10(178)) − 450.
- log10(48) = 1.681 and log10(178) = 2.250, giving 495 ÷ 1.0595 − 450 = 17.2%.
Result: An estimated body fat of about 17.2%.
Tips and common mistakes
- Measure the waist at the navel for men and at the narrowest point for women; measure the neck just below the larynx.
- Women also need a hip measurement at the widest point.
- Take each measurement twice with a flexible tape and use the average; 1 cm can shift the result by about 1%.
- Track the trend over time rather than relying on a single reading.
Assumptions & Limitations
- All measurements should be taken snugly with a flexible tape measure at the specific anatomical points the Navy method specifies (waist at the navel, neck just below the larynx).
- The formula was validated primarily on adult populations and may be less accurate for very lean athletes or unusual body shapes.
- Circumference-based methods are estimates — DEXA scans, hydrostatic weighing, or bioelectrical impedance devices provide more precise body fat readings.
- Measurement technique significantly affects accuracy; inconsistent tape placement is the most common source of error.
Measurement quality matters
Circumference formulas estimate body composition from tape measurements; they do not directly measure fat mass. Small differences in tape position or tension can change the result, so repeat measurements under similar conditions and focus on trends rather than a single reading.
Body-fat estimates from different methods are not interchangeable. Tape methods, bioelectrical impedance, skinfolds and imaging methods can produce different values, so use the same method consistently when tracking change.
Sources and review
Method: U.S. Navy circumference method (metric form), using height, neck, waist and, for women, hip measurements.
Sources:
- Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy men and women from body circumferences and height. Naval Health Research Center, Reports 84-11 and 84-29, 1984.
Last reviewed: October 2026 by Faheem Ali, founder of CalculatorAnything. The method and examples are provided for transparency; results remain estimates and may contain errors.
Results are estimates for general information and screening, not a diagnosis or medical advice. Talk to a qualified healthcare professional before making health or diet decisions. Spotted an error? Tell us — see our editorial policy for how corrections are handled.