Body Fat Calculator (US Navy Method)
Estimate body fat percentage using the US Navy circumference method — validated to within ±3-4% of DXA scans, requiring only a tape measure. Different formulas for men (neck + waist) and women (neck + waist + hip) account for gender differences in fat distribution. Get your body fat category, lean mass, and fat mass breakdown.
What does this tool do?
The Body Fat Calculator uses the US Navy's validated tape-measure method to estimate body fat percentage. It requires neck and waist circumference for men, plus hip circumference for women. The method was developed by the US Navy for fitness assessments and validated against DXA (dual-energy X-ray absorptiometry) with accuracy of ±3-4%. Results include body fat percentage, category (essential, athletic, fitness, average, obese), and if body weight is provided, lean body mass and fat mass in kg/lb. A visual badge shows fat distribution pattern.
How it works
The US Navy method uses regression equations developed from DXA comparisons. Men's formula: %BF = 86.010×log10(waist-neck) - 70.041×log10(height) + 36.76. Women's formula: %BF = 163.205×log10(waist+hip-neck) - 97.684×log10(height) - 78.387. All measurements in cm, using log base 10. The formulas account for the fact that as waist grows relative to neck, body fat increases. Height normalizes for body size. Categories use standard ranges: men essential 2-5%, athletic 6-13%, fitness 14-17%, average 18-24%, obese ≥25%; women essential 10-13%, athletic 14-20%, fitness 21-24%, average 25-31%, obese ≥32%.
Features
- US Navy circumference method (validated against DXA)
- Separate male / female formulas
- Metric (cm/kg) or imperial (in/lb) input
- Body-fat category with color indicator
- Lean body mass and fat mass breakdown
- Visual fat-distribution badge
- Based on US DoD research
How to use
- 1
Select sex and units
Men: neck + waist only. Women: neck + waist + hip. Choose metric or imperial based on your tape measure.
- 2
Measure circumferences
Neck: below larynx, sloping slightly downward. Waist men: at navel. Waist women: at narrowest point. Hip women: at widest point. Measure relaxed, not flexed.
- 3
Enter height and weight (optional)
Height is required for calculation. Weight unlocks lean mass and fat mass breakdown in absolute kg/lb.
- 4
Review results
Body fat percentage, category, and if weight provided, how many kg/lb are fat vs lean tissue.
Common use cases
Fitness progress tracking
Track body composition changes during diet and exercise programs more meaningfully than scale weight alone.
Health risk assessment
Higher body fat, especially abdominal fat, correlates with health risks. The waist measurements capture this.
Athletic goal setting
Target specific body fat ranges for athletic performance (endurance vs strength sports have different optima).
Before expensive testing
Get a reasonable estimate before investing in DEXA scans, bod pod, or hydrostatic weighing for professional assessment.
Tips & best practices
- Measure in the morning after bathroom, before eating, for consistency. Measure at the same time of day for tracking progress
- Don't pull the tape too tight or leave it loose — it should contact skin without compressing tissue
- Accuracy is ±3-4% vs DXA — excellent for a free tape-measure method, but not as precise as clinical methods
- Waist-to-height ratio may be an even better health predictor than body fat percentage — measure waist at navel, divide by height, aim for <0.5