How to use
Choose your sex and enter your weight, height and tape-measure readings. You’ll see your body fat percentage by the U.S. Navy method, the category it falls into and how much of your weight is fat versus lean mass.
How to measure
- Neck — just below the Adam’s apple, with the tape sloping slightly down at the front.
- Waist — men at the navel, women at the narrowest point. Don’t suck in; measure after breathing out.
- Hips (women only) — around the widest part of the buttocks.
Keep the tape snug but not tight. Measure two or three times and use the average.
Formula
The method was developed at the Naval Health Research Center (Hodgdon and Beckett, 1984). The calculator uses the original formulas in centimeters; inches are converted first:
- Men:
body fat % = 495 / (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450 - Women:
body fat % = 495 / (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.221 × log10(height)) − 450
A 5′10″ man with a 15″ neck and 34″ waist comes out at about 17.4%. The simplified inch formulas you may see elsewhere give a slightly different number (17.5%).
Body fat ranges (ACE)
| 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%+ |
Ranges from the American Council on Exercise.
FAQ
How accurate is it? Typically within 3–4 percentage points of lab methods such as DEXA. That’s good enough to track progress — just measure the same way at the same time of day.
Why is body fat better than BMI? BMI can’t tell muscle from fat, while this method relies on girths that grow mostly with fat. A muscular athlete with an “overweight” BMI can have perfectly healthy body fat.
The result is an estimate, not a diagnosis.