Body Fat Calculator
Estimate your body fat percentage using the US Navy circumference method, cross-checked against a BMI-derived estimate. Takes 60 seconds with just a tape measure.
Both methods are estimates, not medical diagnoses. Circumference-based methods can be off by ±3-4% compared to DEXA or hydrostatic weighing, and accuracy decreases at the extremes (very lean or very high body fat). Measurement technique matters — measure at the same time of day, without clothing compressing the tape. If you have health concerns related to body composition, consult a healthcare provider rather than relying on this calculator alone.
Ready to Calculate
Estimate your body fat percentage using the US Navy circumference method, cross-checked against a BMI-derived estimate. Takes 60 seconds with just a tape measure.
Body Fat Calculator Guide
Body fat percentage is a better measure of body composition than weight or BMI alone, since it separates fat mass from lean mass (muscle, bone, organs, water). This calculator gives you two independent estimates so you can see how they compare.
The US Navy Circumference Method
Developed by Hodgdon & Beckett (1984) for military body-composition screening, this method estimates body density from neck, waist, and (for women) hip circumference, then converts it to a body fat percentage using the Siri equation. It requires only a tape measure and is accurate to within roughly ±3-4% of DEXA scan results for most people.
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
BMI-Derived Body Fat % (Deurenberg Formula)
This method estimates body fat from BMI, age, and sex — no tape measure needed — using the formula published by Deurenberg et al. (1991). It's convenient, but tends to overestimate body fat in muscular individuals and underestimate it in older adults who've lost muscle mass, since it can't distinguish fat mass from lean mass.
Body Fat Categories
The American Council on Exercise (ACE) categorizes body fat into essential fat, athletic, fitness, average, and obese ranges, with different thresholds for men and women since women carry more essential fat for reproductive function.
Accuracy & Limitations
Both methods are estimates, not medical diagnoses. Circumference-based methods can be off by ±3-4% compared to DEXA or hydrostatic weighing, and accuracy decreases at the extremes (very lean or very high body fat). Measurement technique matters — measure at the same time of day, without clothing compressing the tape. If you have health concerns related to body composition, consult a healthcare provider rather than relying on this calculator alone.
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Body Fat Calculator FAQ
How accurate is the Navy body fat method?
Studies comparing the Navy circumference method to DEXA scans generally find it accurate to within ±3-4% for most adults, though accuracy decreases for very lean or very high body fat individuals, and for people with atypical body proportions.
Why do the Navy and BMI-derived results differ?
The Navy method measures your actual body shape via circumferences, while the BMI-derived formula only uses weight, height, age, and sex. A muscular person will have a normal Navy result but an inflated BMI-derived result, since BMI can't tell muscle from fat.
Where exactly should I measure my waist?
Men measure at the navel. Women measure at the narrowest point of the natural waist, usually just above the belly button. Measure without pulling the tape tight and without holding your breath.
Can this calculator replace a DEXA scan or caliper test?
No — DEXA scans and skinfold caliper tests performed by a trained professional are more accurate. This calculator is a free, convenient way to track trends over time between more precise measurements, not a diagnostic tool.