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Body Fat % Calculator

Estimate your body fat percentage using the US Navy method — only a tape measure required.

Estimated Body Fat
Men: %BF = 86.01×log(waist−neck) − 70.041×log(height) + 36.76 Women: %BF = 163.205×log(waist+hip−neck) − 97.684×log(height) − 78.387 (All measurements in inches, log = log base 10)

The US Navy method is the standard fitness assessment tool used by the US military. It's less precise than DEXA scans but requires only a tape measure and is accurate within ±3-4 percentage points for most people.

Male BF% (waist A1, neck B1, height C1)
=86.01*LOG10(A1-B1)-70.041*LOG10(C1)+36.76

How to Measure Accurately

Measurement technique matters significantly for the US Navy method. Waist: measure at the navel (belly button level) — not the narrowest point of your torso. Keep the tape horizontal, parallel to the floor, and snug but not compressing the skin. Take the measurement at the end of a normal exhale, not a sucked-in position.

Neck: measure just below the larynx (Adam's apple), sloping slightly downward toward the front. Keep the tape perpendicular to the neck's long axis. Hip (women only): measure around the widest part of the hips and buttocks, keeping the tape horizontal.

Take each measurement twice and average the results. If the two measurements differ by more than 0.5 inches, take a third and use the median. Consistent technique across measurements over time is more important than any single reading — trends matter more than absolute values.

Body Fat Categories by Sex

For men: Essential fat 2-5% (minimum for physiological function), Athlete 6-13%, Fitness 14-17%, Average 18-24%, Obese 25%+. For women: Essential fat 10-13%, Athlete 14-20%, Fitness 21-24%, Average 25-31%, Obese 32%+. Women naturally carry more essential fat due to hormonal and reproductive physiology.

These categories are population-based guidelines, not clinical diagnoses. An athlete at 14% body fat and a sedentary person at 14% body fat have the same percentage but very different health profiles. Body fat percentage is one useful data point; fitness level, metabolic health markers (blood glucose, lipid panel), and functional capacity are equally or more important.

Frequently Asked Questions

The US Navy method has approximately ±3-4 percentage points error compared to DEXA scans, the gold standard. It systematically overestimates body fat in lean individuals and underestimates in very obese individuals. It is most accurate in the middle ranges (15-30%). For tracking changes over time, it is useful — a 3-point drop over 3 months is meaningful even if the absolute number is imprecise.
DEXA (dual-energy X-ray absorptiometry) scan: ±1-2% accurate, also measures bone density. Hydrostatic (underwater) weighing: very accurate but requires full submersion. Bod Pod (air displacement): similar to hydrostatic, less invasive. Bioelectrical impedance (BIA) — handheld devices, scale-based: highly variable (±3-8%) depending on hydration status. Consumer methods rank: DEXA > Bod Pod ≥ hydrostatic > US Navy > BIA.
BMI cannot distinguish muscle from fat. A muscular person with low body fat may be classified as "overweight" or "obese" by BMI. Body fat percentage directly measures the proportion of fat to total body mass, which is more closely linked to metabolic health outcomes than BMI for individuals.
For men, abdominal definition (visible "four-pack") typically begins around 14-17% body fat. A clear six-pack generally requires 10-13%. For women, definition begins around 20-22% and six-pack visibility requires 16-19%. Genetic fat distribution affects where fat is lost last — some people see abs at higher body fat percentages than others.