Body Fat Calculator
Estimate your body fat percentage using the US Navy method — just a tape measure. Get your category, fat mass, and lean mass.
The Navy method is a tape-measure estimate. Real body fat varies ±3% from the result. For higher precision, use a DEXA scan (±1%). Measure in the morning, standing relaxed, with the tape taut but not compressing skin.
What body fat percentage actually tells you
Body fat percentage shows how much of your body weight is stored fat versus lean tissue (muscle, bone, water, organs). It's a more useful health marker than BMI or scale weight alone — two people at the same weight can have dramatically different body fat percentages, and dramatically different health risks.
Why the Navy method works
Developed in the 1980s for US Navy fitness screening, the formula uses a waist-to-neck ratio (and hip measurement for women) to estimate body fat. It's empirically calibrated against hydrostatic weighing and has been validated in multiple peer-reviewed studies. Not perfect, but surprisingly effective given it needs just a tape measure.
How to get reliable measurements
Measure in the morning, before eating, in minimal clothing. Use a fabric tape measure (not rigid). Stand relaxed with arms at your sides. For the waist, men measure at the narrowest point (usually just above the navel); women measure at the natural waist or the level of the navel. Neck measurement is taken just below the larynx. Hip measurement (women) is at the widest point. Same technique every time — consistency matters more than perfection.
What to do with the number
Track body fat monthly to gauge whether you're losing fat or muscle during a cut, or gaining muscle or fat during a bulk. The scale alone lies — you can lose 5 lb and look worse (mostly muscle lost) or gain 5 lb and look better (mostly muscle gained). Combined with scale weight, body fat shows what's really happening.
Methods that are more accurate (but less convenient)
DEXA scan: Gold standard, $50-$150 per scan, gives ±1% accuracy and breaks down fat distribution regionally. BOD POD / hydrostatic weighing: Clinical setting, ±2%, requires a pool or specialized equipment. Caliper skinfolds: Cheap, ±3-5% with good technician. Bioimpedance scales: Varies wildly, ±5-8%, strongly affected by hydration. For most people, Navy tape + monthly tracking is the right balance of accuracy and practicality.
Frequently asked questions
How accurate is the US Navy method?▾
Within about ±3% of the true value for most people. It's not as accurate as DEXA (±1%) or underwater weighing, but it's dramatically better than most consumer bioimpedance scales, completely free, and requires only a tape measure. Measurement technique matters — sloppy measurements produce sloppy estimates.
Why do I need to measure my neck?▾
The Navy method uses the waist-to-neck ratio (and hip for women) as a proxy for body fat distribution. Neck circumference is tightly correlated with lean mass and relatively insensitive to small measurement errors, making it a stable anchor for the formula.
What's a healthy body fat percentage?▾
Men: 8-20% is healthy; 6-13% is athletic; under 5% is unsustainable. Women: 21-33% is healthy; 14-20% is athletic; under 12% often disrupts hormonal health. These ranges vary by age and individual physiology — older adults naturally carry slightly more fat than the 'fitness' numbers suggest.
How should I measure?▾
In the morning, before eating, wearing minimal clothing. Use a flexible tape, not a rigid one. Stand relaxed with good posture. Waist: at the narrowest point (men) or at the navel (women). Neck: just below the Adam's apple (men) or the middle of the neck (women). Hip (women): at the widest point of the hips. Don't compress the skin; the tape should be snug but not tight.
Is body fat more important than weight?▾
Arguably yes. BMI doesn't distinguish muscle from fat; body fat percentage does. Two 180 lb men can have wildly different body composition — one at 12% body fat (muscular) vs 28% (carrying excess fat). Health outcomes correlate more with body fat percentage and waist circumference than with scale weight alone.
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