Body Fat Calculator
Estimate body fat percentage using the US Navy tape-measure method.
What this calculator does
Estimates body fat percentage from a few circumference measurements — height, neck, waist, and (for women) hip — using the US Navy method, a widely-used non-invasive alternative to calipers or scans.
Who this is for
Anyone wanting a more informative body composition measure than BMI alone, people tracking body recomposition (muscle gain alongside fat loss) where scale weight and BMI alone can be misleading, or anyone without access to a DEXA scan or hydrostatic weighing wanting a reasonable estimate.
How this calculator works
The US Navy method estimates body fat from circumference measurements rather than skinfold calipers or DEXA scans. It's reasonably accurate for most body types but less reliable at the extremes (very lean athletes or very high body fat).
The formula
For men: Body Fat% = 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450. For women, hip circumference is added to the waist-neck calculation, reflecting the different typical fat distribution pattern.
Worked example
A man with a 38cm neck, 85cm waist, and 175cm height: waist minus neck = 47cm. Plugging into the formula gives 16.9% body fat — solidly in the "fitness" category for most reference charts, illustrating how the calculation weighs waist size relative to neck and height rather than raw body weight.
Typical Body Fat Categories
| Category | Men | Women |
|---|---|---|
| Essential fat | 2-5% | 10-13% |
| Athletes | 6-13% | 14-20% |
| Fitness | 14-17% | 21-24% |
| Acceptable/average | 18-24% | 25-31% |
| Obese | 25%+ | 32%+ |
Women naturally carry more essential body fat than men — this isn't a health difference but a physiological one, related to reproductive function, which is why the category thresholds are consistently higher for women across the whole scale, not just at the extremes.
Where you fall on the scale
Run the calculator above to see where your body fat percentage sits across standard categories.
Common mistakes
- Measuring inconsistently. Circumference measurements need to be taken at the same spot, same time of day, and same tension each time — small measuring errors meaningfully shift the result.
- Expecting DEXA-level precision. The Navy method has a margin of error of a few percentage points — trust the trend over repeated measurements more than any single reading.
- Not accounting for hydration and food intake. Waist measurements can shift noticeably based on when you last ate or drank — measure at a consistent time, like first thing in the morning.
- Measuring waist at the wrong spot. The standard measurement point is at the navel, not at the narrowest point of the torso — using the wrong spot skews the result meaningfully in either direction.
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Frequently Asked Questions
How accurate is the US Navy method compared to a DEXA scan?
It's generally within a few percentage points of DEXA for most body types, though accuracy decreases at the extremes — very lean athletes and people with very high body fat tend to see larger discrepancies. It's best used to track trends over time rather than as a single precise reading.
Where exactly should I measure my waist?
At the navel (belly button) level, not at the narrowest point of your torso — this is the standard reference point for the US Navy method and using a different spot will skew your result.
Why do I need hip measurements as a woman but not as a man?
The Navy method formula differs by sex because fat distribution patterns differ — the women's formula was calibrated using hip circumference as an additional variable to improve accuracy.
What's a healthy body fat percentage?
Roughly 14-24% for men and 21-31% for women falls in the fitness-to-average range on most reference charts. Essential fat minimums are lower for men (2-5%) than women (10-13%) due to physiological differences.
Why is the "acceptable" body fat range higher for women than men?
Women naturally carry more essential body fat than men for physiological reasons related to reproductive function — this is a normal biological difference, not a health disparity, which is why every category threshold runs higher for women across the whole scale.
Is being an "athlete" body fat percentage always the goal?
Not necessarily — very low body fat percentages can be appropriate for competitive athletes but aren't a universal target, and extremely low levels can carry their own health considerations. The "fitness" and "acceptable" categories represent healthy ranges for most people, not just the athlete tier.