How to Calculate Your Body Fat Percentage (US Navy Method)
The US Navy method estimates your body fat percentage from three tape measurements: height, neck, and waist (plus hip for women). No scale, no scan, no calipers. A man who is 178 cm tall with a 40 cm neck and a 90 cm waist comes out to 18.7% body fat, which lands in the “Average” category. The same formula, applied to different numbers, is what the calculator below runs.
How the method works
Circumference measuring wraps a flexible tape around a few key points on the body, then runs those numbers through a formula the US Navy developed in the 1980s as a cheap alternative to underwater weighing. It won’t match a DEXA scan exactly, but it needs nothing more than a tape measure and a few minutes, which is why gyms, trainers, and the military still use it today.
The formula differs by sex because men and women store fat differently, and each equation comes from separate research.
Men:
body fat % = 495 / (1.0324 - 0.19077 x log10(waist - neck) + 0.15456 x log10(height)) - 450Women:
body fat % = 495 / (1.29579 - 0.35004 x log10(waist + hip - neck) + 0.221 x log10(height)) - 450All measurements go in centimeters. Only the women’s formula needs a hip measurement, since it accounts for a fat distribution pattern the men’s formula doesn’t need to model.
Here’s where a given percentage falls:
Men
| Body fat % | Category |
|---|---|
| Below 6% | Essential fat |
| 6% to 13.9% | Athletes |
| 14% to 17.9% | Fitness |
| 18% to 24.9% | Average |
| 25% and above | Obese |
Women
| Body fat % | Category |
|---|---|
| Below 14% | Essential fat |
| 14% to 20.9% | Athletes |
| 21% to 24.9% | Fitness |
| 25% to 31.9% | Average |
| 32% and above | Obese |
Worked example: 178 cm, 40 cm neck, 90 cm waist
Here’s the full calculation for a man who is 178 cm tall, with a 40 cm neck and a 90 cm waist.
| Step | Calculation | Result |
|---|---|---|
| Trunk value: waist minus neck | 90 - 40 | 50 cm |
| log10 of the trunk value | log10(50) | 1.699 |
| log10 of height | log10(178) | 2.250 |
| Denominator | 1.0324 - (0.19077 x 1.699) + (0.15456 x 2.250) | 1.0562 |
| Divide 495 by the denominator | 495 / 1.0562 | 468.66 |
| Subtract 450 | 468.66 - 450 | 18.7% |
That 18.7% sits in the “Average” band for men. It’s also close enough to the top of Fitness (17.9%) that a small change in waist size would move him into the band above.
Not hypothetical. Here’s the same man, only the waist changes:
| Waist | Body fat % | Category |
|---|---|---|
| 85 cm | 14.9% | Fitness |
| 90 cm | 18.7% | Average |
| 95 cm | 22.2% | Average |
Five centimeters off the waist alone moves him from Average into Fitness. Waist carries most of the weight in this formula, so a loose or overly snug tape reading shifts the result more than people expect.
Neck size matters too, in the opposite direction. Keep the waist fixed at 90 cm and change only the neck:
| Neck | Body fat % |
|---|---|
| 40 cm | 18.7% |
| 42 cm | 17.2% |
A thicker neck lowers the estimate, because the formula uses waist minus neck as its trunk value. Measure the neck too high or too low on the throat and you’ll shift that trunk number without realizing it.
Add a body weight and the calculator converts the percentage into actual mass. At 80 kg and 18.7% body fat, fat mass is 80 x 0.187 = 15.0 kg, and lean mass is the remaining 80 - 15.0 = 65.0 kg.
Calculate with your own numbers
Enter your height, neck, and waist (plus hip if you selected female), and get your body fat percentage and category instantly. The math runs in your browser; nothing is sent anywhere.
Common mistakes and limitations
Measuring over clothing. A shirt or waistband adds slack the tape can’t tell apart from actual body circumference. Measure directly against skin for a number you can trust.
Not keeping the tape level and snug. A tape that dips at the back or sits at an angle reads shorter than the real circumference, which pushes the calculated percentage down artificially. It should sit snug against the skin, level all the way around, without pulling tight enough to compress tissue.
Confusing body fat percentage with BMI. These measure different things. BMI is only weight divided by height squared, so it can’t tell fat from muscle: a heavily muscled person can post a high BMI despite low body fat. The Navy method measures actual circumference, so it responds to real changes in fat and muscle rather than just the number on a scale.
Skipping the hip measurement for women. Women typically carry more fat around the hips than men do, so the women’s formula adds a hip term the men’s formula doesn’t need. Using the men’s formula on a woman, or leaving hip out of the women’s formula, produces a number that doesn’t reflect how fat is actually distributed.
Trusting the number at the extremes. The formula was built from population averages, so it’s least accurate for people who are very lean, very heavy, or otherwise far from a typical build. Competitive bodybuilders and athletes with unusual body proportions should treat the result as a rough estimate rather than an exact figure.
Frequently asked questions
How accurate is the Navy method? For most people, it lands within about 3 to 4 percentage points of a DEXA scan, the imaging-based method used as the accuracy benchmark. That’s close enough to track trends over time, though it gets less reliable at the extremes: very lean athletes and people carrying a lot of excess weight tend to see larger gaps between the tape estimate and a scan.
What is a healthy body fat percentage? It depends on sex and goals. For men, 6% to 13.9% is typically seen in athletes, 14% to 17.9% is a solid fitness range, and 18% to 24.9% covers most healthy adults classified as average. For women, the ranges run higher: 14% to 20.9% for athletes, 21% to 24.9% for fitness, and 25% to 31.9% for average. Essential fat, the minimum needed for normal body function, sits below 6% for men and below 14% for women.
Is body fat percentage the same as BMI? No. BMI only uses height and weight, so it can’t separate fat from muscle. The Navy method measures actual circumference at the neck, waist, and (for women) hip, so it captures real differences in body composition that BMI misses entirely. Two people with the same BMI can have very different body fat percentages.
How does the formula work for women? Take a woman who is 165 cm tall with a 34 cm neck, a 74 cm waist, and a 96 cm hip. Running those numbers through the women’s formula gives 26.4% body fat, in the “Average” category. At a body weight of 65 kg, that works out to 65 x 0.264 = 16.9 kg of fat mass and 65 - 16.9 = 48.1 kg of lean mass. The extra hip term is the only structural difference from the men’s formula.