Body Fat Calculator
Estimate your body fat percentage using the US Navy method or a BMI-based formula. Free, no signup required.
Body measurements (for Navy method)
Measure at the narrowest point (waist), widest point (hip), and below the Adam's apple (neck). Leave blank for BMI-based estimate only.
Why body fat percentage matters more than weight
Two people can weigh exactly 80kg and look completely different. One at 15% body fat carries 68kg of lean mass and 12kg of fat. Another at 30% carries 56kg of lean mass and 24kg of fat — twice the fat, 12kg less muscle. The scale shows the same number, but the bodies are not comparable.
Body fat percentage is a better indicator of health and fitness than scale weight or BMI. It is the number that actually matters for body composition goals — whether you are trying to get leaner, build muscle, or assess your progress over time.
How this calculator estimates body fat
The US Navy method
The Navy method uses circumference measurements — waist, neck, and height (plus hip for women) — to estimate body fat through logarithmic ratios. Developed by Hodgdon & Beckett (1984) for the US Department of Defense, it was validated across large military populations and is accurate to within ±3–4% of DEXA scan results.
The formula works because waist circumference correlates strongly with abdominal fat storage, while neck circumference accounts for lean upper body mass. The ratio between these measurements, adjusted for height, provides a reliable estimate of total body fat percentage.
Hodgdon, JA & Beckett, MB (1984). Prediction of percent body fat for U.S. Navy men and women from body circumferences and height. Naval Health Research Center, Report No. 84-29.
The BMI-based estimate
The Deurenberg formula estimates body fat from BMI, age, and sex. It is less accurate than circumference-based methods because BMI cannot distinguish muscle from fat — a muscular person will get an inflated estimate. This calculator includes it as a rough reference point, not as a primary measurement.
Deurenberg, P et al. (1991). Body mass index as a measure of body fatness: age- and sex-specific prediction formulas. British Journal of Nutrition, 65(2), 105–114.
Limitations of all estimation methods
No circumference-based method is perfectly accurate. The Navy method does not account for limb fat distribution, and BMI cannot distinguish muscle from fat. DEXA scans and hydrostatic weighing remain the gold standard for precision. However, for tracking trends over time, consistent measurements with the same method are more useful than a single highly accurate reading.
Body fat categories explained
Body fat categories differ between men and women because women carry more essential fat for reproductive and hormonal function. Essential fat is the minimum required for physiological health — going below it impairs hormonal function, immune response, and organ protection. There is no single “ideal” body fat percentage; the right target depends on your goals and sport. For most recreational lifters, 10–15% for men and 18–24% for women is a sustainable range that supports both performance and health.
How to measure accurately
Consistency matters more than precision. Measure at the same time of day, under the same conditions, with the same tape. Waist: at the narrowest point (at or above the navel). Neck: below the Adam's apple at the narrowest point. Hip (women): at the widest point of the buttocks. Stand relaxed — do not flex or suck in.
Know your body fat? Use it in Evid.
Entering your body fat percentage in Evid unlocks the Cunningham equation for more accurate TDEE and switches to lean-mass-based protein targets. More data, better results.
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