How the Navy body fat formula works
The US Navy equations, published by Hodgdon and Beckett in 1984, estimate body density from circumferences and height. Waist minus neck (for men) or waist plus hips minus neck (for women) captures how much of your girth is likely to be fat, and height scales it to your frame.
For men: body fat % = 495 / (1.0324 - 0.19077 × log10(waist - neck) + 0.15456 × log10(height)) - 450, with measurements in centimeters. For women: 495 / (1.29579 - 0.35004 × log10(waist + hip - neck) + 0.22100 × log10(height)) - 450.
Worked example: a man who is 178 cm tall with a 38 cm neck and 86 cm waist comes out at about 17% body fat.
How to measure correctly
Small tape errors move the result by a few points, so technique matters more than the formula.
- Neck: just below the larynx (Adam's apple), tape sloping slightly down to the front.
- Waist (men): horizontally at the navel, relaxed, after a normal breath out.
- Waist (women): at the narrowest point of the torso, relaxed.
- Hips (women): at the widest point of the buttocks, feet together.
- Measure twice, in the morning before eating, and use the average.
Body fat percentage chart
These American Council on Exercise ranges are the most widely used way to read a body fat number. Healthy ranges rise a little with age.
| Category | Men | Women |
|---|---|---|
| Essential fat | 2-5% | 10-13% |
| Athletic | 6-13% | 14-20% |
| Fit | 14-17% | 21-24% |
| Average | 18-24% | 25-31% |
| High | 25%+ | 32%+ |
How accurate is the Navy method?
Compared with DEXA, circumference methods typically land within about 3-4 percentage points for most people. They tend to overestimate body fat in very muscular people with thick necks and waists, and underestimate it in people who carry fat mainly on the hips and thighs.
Accuracy for a single reading is limited. Consistency across readings is much better, which is why tape methods work well for tracking change: same tape, same spots, same time of day.
Body fat vs BMI
BMI only uses height and weight, so it cannot tell muscle from fat. Two people with a BMI of 27 can have 15% and 30% body fat. The calculator shows a BMI-based estimate (Deurenberg equation) next to the Navy result: if your Navy number is clearly lower, you likely carry more muscle than average for your size.
How to lower body fat
Fat loss comes from a sustained calorie deficit. Keeping muscle while you lose it comes from enough protein (around 1.6-2.2 g per kg of body weight) and strength training two to four times a week.
Expect about 0.5-1% of body weight per week at most. Re-measure every two to four weeks. Waist usually moves before the scale does, which is why measurements are worth tracking alongside weight.
Healthy body fat percentage by age
Body fat naturally rises a little with age, so a healthy range for a 60-year-old is higher than for a 25-year-old. These ranges come from a study that linked body fat to healthy BMI ranges in adults of different ages (Gallagher et al., 2000).
| Age | Women | Men |
|---|---|---|
| 20-39 | 21-33% | 8-20% |
| 40-59 | 23-34% | 11-22% |
| 60-79 | 24-36% | 13-25% |
Navy vs Army body fat calculator
The Navy method measures several sites: neck and waist, plus hips for women. Since 2023 the US Army uses its own one-site tape test instead, based on waist circumference at the navel and body weight, to check its fitness standards.
For tracking your own progress, either works. What matters is using the same method, the same tape and the same spots every time. If you need the Army's standard, use our Army body fat calculator instead.