Quick answer: This calculator uses the US Navy (Hodgdon–Beckett) method: men: 86.010×log10(waist−neck) − 70.041×log10(height) + 36.76; women: 163.205×log10(waist+hip−neck) − 97.684×log10(height) − 78.387. Measure in inches or cm below.
Last reviewed: September 2026
Key facts
- Body fat % measures fat mass vs total mass — a better health indicator than weight alone.
- The US Navy method (tape measurements) is accurate to about ±3–4% vs DEXA scans.
- Measure the waist at the navel, not at the belt line — this is the most common mistake.
- Healthy ranges: roughly 10–20% for men and 20–30% for women.
This free body fat percentage calculator uses the US Navy circumference method — just your waist, neck, hip and height — plus a BMI-based backup. Get your body fat %, fitness category and healthy-range comparison instantly. Track it monthly to see real composition change.
More accurate than the scale alone: two people at the same weight can have very different fat percentages. Track this monthly to see real composition change.
How to use
- Choose the US Navy tape method (recommended) or the BMI estimate.
- Select sex and units (inches or cm), then enter your measurements — relax, do not suck in.
- Measure the waist at the navel and the neck just below the larynx; women also measure the hip at its widest.
- Read your body fat % and fitness category.
The US Navy formulas
Women: 163.205×log₁₀(waist+hip−neck) − 97.684×log₁₀(height) − 78.387
| Term | Meaning |
|---|---|
| waist − neck | Belly fat proxy: abdominal girth minus lean neck tissue. |
| hip (women) | Included because women store more fat at the hips. |
| height | Normalises for frame size; all in the same units. |
Worked examples
Man: waist 36 in, neck 16 in, height 70 in
waist − neck = 20, log₁₀(20) = 1.301, log₁₀(70) = 1.845. 86.010 × 1.301 − 70.041 × 1.845 + 36.76 = 111.90 − 129.23 + 36.76 = 19.4% — average range.
Woman: waist 30 in, hip 40 in, neck 14 in, height 65 in
waist + hip − neck = 56, log₁₀(56) = 1.748, log₁₀(65) = 1.813. 163.205 × 1.748 − 97.684 × 1.813 − 78.387 = 285.31 − 177.09 − 78.39 = 29.8% — average range.
Body fat categories
| Category | Men | Women |
|---|---|---|
| Essential fat | < 6% | < 14% |
| Athletic | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Overweight | ≥ 25% | ≥ 32% |
Frequently asked questions
How accurate is the Navy body fat method?
Within about ±3–4% of a DEXA scan for most people — far better than BMI for muscular builds. Accuracy depends on honest, relaxed measurements; sucking in your stomach skews the result.
Why does the formula use logarithms?
Fat distribution scales non-linearly with body size, so the Navy researchers fitted logarithmic terms to underwater-weighing data. The logs keep the estimate accurate across small and large frames alike.
Where exactly do I measure my waist?
At the navel (belly button), with the tape horizontal and snug but not compressing the skin. Measuring at the belt line or over clothing gives falsely low readings.
What is a healthy body fat percentage?
Roughly 10–20% for men and 20–30% for women. Athletes sit lower; going below essential fat (6% men, 14% women) risks hormonal and immune problems.
Why not just use BMI?
BMI cannot distinguish muscle from fat, so athletes often read as “overweight”. The Navy method uses actual girths, making it far more meaningful for muscular or very lean people.
Sources
- ACE Fitness — Body fat percentage charts and measurement guidance
- NIH — Body composition assessment references
Key takeaways
- Navy method: waist, neck, (hip), height — accurate to ±3–4%.
- Measure at the navel, relaxed, over bare skin.
- Healthy: ~10–20% men, ~20–30% women.
- BMI is a rough backup; the tape method beats it.
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