A body fat calculator estimates your body fat percentage using the US Navy circumference method, a standardized formula based on body measurements rather than body weight. Enter your sex, height, neck, and waist (plus hip for women), and the calculator returns an estimated body fat percentage.
Useful as a screening estimate for fitness goals, military readiness standards, or general body-composition awareness. The Navy formula is less accurate than DEXA scans or hydrostatic weighing but significantly better than BMI for distinguishing muscle from fat.
Key takeaway
Body fat percentage tells you what BMI cannot, how much of your weight is fat versus muscle, bone, and organs. Two people with the same BMI can have very different metabolic profiles and visual appearances. The US Navy formula trades a small amount of accuracy for ease of measurement (just a tape measure needed) and is the standard tool for circumference-based body fat estimation.
How it's calculated
The US Navy formula uses logarithm-based equations that depend on sex:
Men: BF% = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76
Women: BF% = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387
All inputs in inches. The men's formula uses just waist minus neck because abdominal fat is the main male adiposity site; the women's formula adds the hip measurement because women carry fat more evenly across the lower body.
Reference body fat ranges (American Council on Exercise):
| Category | Men | Women |
|---|---|---|
| Essential fat | 2-5% | 10-13% |
| Athletes | 6-13% | 14-20% |
| Fitness | 14-17% | 21-24% |
| Average | 18-24% | 25-31% |
| Obese | 25%+ | 32%+ |
These bands are general guidelines, not health verdicts. Body composition norms shift with age (older adults naturally carry more fat) and ethnicity. The Navy formula's accuracy varies by individual, typical error is ±3-4% body fat against gold-standard DEXA, but can be larger for very muscular or very lean people.
Source: US Navy circumference-based body fat formula (Hodgdon and Beckett, 1984)
Examples
5'10" man, 15" neck, 34" waist
- Sex Male
- Height 70 in
- Neck circumference 15 in
- Waist circumference 34 in
- Hip circumference (women only) 0 in
A 5'10" man with a 15" neck and 34" waist comes in at about 17.6% body fat by the Navy formula, within the "fitness" range (14-17%) per ACE bands, just on the higher edge. Useful starting point for someone who's measured themselves but lacks a clear body-comp picture.
5'5" woman, 13" neck, 28" waist, 38" hips
- Sex Female
- Height 65 in
- Neck circumference 13 in
- Waist circumference 28 in
- Hip circumference (women only) 38 in
A 5'5" woman with these measurements estimates to 25.9% body fat, at the boundary between the "fitness" (21-24%) and "average" (25-31%) ranges for women per ACE bands. The Navy formula's hip-measurement requirement for women captures lower-body fat distribution that men's formula skips.
Frequently asked questions
How accurate is the US Navy body fat formula?
Typically within ±3-4% body fat of gold-standard DEXA measurement for most adults. Less accurate at extremes (very lean athletes, very heavy individuals) and across some ethnicities (the original validation was on US Navy personnel, skewing toward young, fit, US-population body types). Better than BMI for distinguishing muscle from fat, worse than DEXA or hydrostatic weighing.
What body fat percentage is healthy?
Depends on age, sex, and goals. ACE reference ranges put healthy "fitness" levels at 14-17% for men and 21-24% for women. Below that is athletic / lean; above that is average / overweight. Essential fat (the minimum needed for organ function) is 2-5% for men and 10-13% for women, going below those levels is dangerous, especially for women whose hormonal cycles depend on adequate fat stores.
Why are women's healthy body fat ranges higher than men's?
Women evolved with higher essential fat stores to support pregnancy, breastfeeding, and hormonal cycles. The healthy range difference (women 7-10% higher than men at any given fitness category) reflects this biological reality, not a different standard for fitness. A male athlete at 8% body fat and a female athlete at 17% are at equivalently lean, healthy points for their respective biology.
What's the best way to lower body fat percentage?
Two levers: reduce body fat mass (calorie deficit + protein
- cardio) or increase lean mass (resistance training + adequate protein + sleep). Combining both is most effective. Body fat percentage = fat mass ÷ total mass, adding 5 lb of muscle drops the percentage even at the same fat mass. For sustainable change, target 0.5-1% body fat reduction per month rather than aggressive cuts.