Health
Body Fat Calculator
Knowing your body fat percentage is genuinely more useful than knowing your weight or BMI — it distinguishes lean mass from fat mass, which matters for body composition goals, fitness benchmarks, and health risk. DEXA scans are the gold standard at ~$100-150 per scan. Bioelectrical impedance scales are convenient but volatile (±5% reading variance day to day based on hydration). The US Navy tape-measure method, developed in the 1980s for military body composition standards, costs $0 and lands within ±3% of DEXA for most people. This calculator uses the official Navy formula: men need neck + waist measurements; women need neck + waist + hip.
How to take the measurements correctly
Use a flexible cloth or fiberglass tape measure (not metal, not stretchy fabric). Take measurements first thing in the morning before eating or drinking. Keep the tape snug against skin but not compressing it.
- Neck: just below the larynx (Adam's apple area), tape level and parallel to the floor.
- Waist (men): at the navel level, relaxed (don't suck in).
- Waist (women): at the narrowest point of the natural waist, usually just above the navel.
- Hip (women only): at the widest part of the hips/buttocks.
Take each measurement three times and use the average. Differences of 0.5 inch are noise; differences of 1+ inch mean re-measure.
Body fat ranges by category
| Category | Men | Women |
|---|---|---|
| Essential (minimum healthy) | 2-5% | 10-13% |
| Athletes | 6-13% | 14-20% |
| Fitness (lean, visible muscle) | 14-17% | 21-24% |
| Average | 18-24% | 25-31% |
| Obese | 25%+ | 32%+ |
Most men land in 18-24% (average) until they start lifting and eating intentionally; sub-15% requires sustained effort. Most women land in 25-31%; sub-22% requires consistent training and nutrition discipline.
How to use this calculator
- Sex: male or female (different formulas).
- Height in inches.
- Neck: measured per instructions above.
- Waist: at navel (men) or natural waist (women).
- Hip (women only): widest part of hips.
- Output: body fat percentage + category.
- Re-measure monthly, not daily — changes happen slowly and short-term tape variance is high.
Common scenarios
180-lb male, 5'10", neck 15", waist 34". Navy formula: ~16.7% body fat. Fitness category — visible muscle definition, healthy weight.
150-lb female, 5'5", neck 13", waist 28", hip 38". Navy formula: ~24% body fat. Fitness category — healthy weight, athletic build.
220-lb male, 5'10", neck 17", waist 42". ~27% body fat. Obese category. Significant weight loss + strength training would put this person in 18-20% range over 6-12 months.