The U.S. Navy body fat calculator estimates your body fat percentage from your height and a few tape-measure readings: neck and waist for men, plus hips for women. A man who is 178 cm tall with a 39 cm neck and an 86 cm waist comes out at 16.4% body fat, which falls in the Fitness range for men. No scale, calipers or lab visit is needed.
Our free Navy body fat calculator applies the formula as you type and shows your percentage next to a table of body fat categories. This guide explains the formula, how to take each measurement correctly, how accurate the method is and what to do with the result.
The U.S. Navy body fat formula
The U.S. Navy developed this circumference method to screen personnel quickly with nothing more than a tape measure. With all measurements in centimeters, the formulas are:
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) + 0.22100 × log10(height)) − 450The idea is that a larger waist relative to the neck usually means more stored fat, while height scales the result to your frame.
Worked example: a man, 178 cm, neck 39 cm, waist 86 cm
- Waist minus neck: 86 − 39 = 47. log10(47) = 1.6721.
- log10(178) = 2.2504.
- Divisor: 1.0324 − (0.19077 × 1.6721) + (0.15456 × 2.2504) = 1.0324 − 0.3190 + 0.3478 = 1.0612.
- 495 ÷ 1.0612 = 466.44, and 466.44 − 450 = 16.4% body fat.
Worked example: a woman, 165 cm, neck 33 cm, waist 72 cm, hips 98 cm
- Waist plus hip minus neck: 72 + 98 − 33 = 137. log10(137) = 2.1367.
- log10(165) = 2.2175.
- Divisor: 1.29579 − (0.35004 × 2.1367) + (0.22100 × 2.2175) = 1.29579 − 0.74794 + 0.49006 = 1.0379.
- 495 ÷ 1.0379 = 476.92, and 476.92 − 450 = 26.9% body fat, in the Average range for women.
How to take your measurements
The formula is only as good as the tape readings, and a single centimeter on the waist moves the result by roughly half a point to three-quarters of a point. Use a flexible tape that does not stretch, measure on bare skin, and stand relaxed without pulling your stomach in.
- Height: barefoot, standing straight against a wall.
- Neck: just below the larynx (Adam's apple), with the tape sloping slightly down toward the front.
- Waist: men measure horizontally at the level of the navel. Women measure at the narrowest point of the waist.
- Hip (women only): around the widest part of the buttocks, keeping the tape level.
Pull the tape snug without pressing into the skin. Take each measurement two or three times and use the average. The calculator works in centimeters, so convert inches first by multiplying by 2.54, or use the length converter: a 34-inch waist is 86.4 cm.
Body fat categories
The calculator labels your result using the American Council on Exercise (ACE) categories, shown in the table beside the result:
| Category | Women | Men |
|---|---|---|
| Below essential fat | Under 10% | Under 2% |
| Essential fat | 10–13.9% | 2–5.9% |
| Athletes | 14–20.9% | 6–13.9% |
| Fitness | 21–24.9% | 14–17.9% |
| Average | 25–31.9% | 18–24.9% |
| Obese | 32% and up | 25% and up |
The calculator rounds your result to one decimal place and then picks the row that figure falls in, so a result shown as 6.0% is in the Athletes range for men. Essential fat is the minimum the body needs for hormones, nerves and organ protection. Women carry more essential fat than men, which is why every range for women sits higher.
How accurate is the Navy method?
For most adults, tape-measure methods like this one land within roughly 3 to 4 percentage points of laboratory methods such as DEXA scans. A result of 20% could therefore reflect a true value anywhere from about 16% to 24%. The error tends to be larger for very lean, very muscular and very heavy people, because the formula assumes a typical body shape.
| Method | What you need | Trade-off |
|---|---|---|
| U.S. Navy tape method | A tape measure | Free and repeatable, but an estimate |
| Skinfold calipers | Calipers and practice | Depends heavily on the tester's skill |
| Bioimpedance scale | A smart scale | Readings shift with hydration |
| DEXA scan | A clinic visit | Most precise of these, but costs money |
The Navy method is most useful for tracking change. Measured the same way each time, a falling waist reading and a falling percentage are a reliable sign of progress even if the absolute number is off by a few points. Treat the result as an estimate, not a medical assessment, and it is not meant for children or during pregnancy.
How to use the body fat calculator
- Open the body fat calculator.
- Choose Male or Female. The Hip field appears when you choose Female.
- Enter your Height, Neck and Waist in centimeters, plus Hip for women. Your waist needs to be larger than your neck, or for women your waist plus hip, for the formula to work; if it is not, the calculator says so instead of showing a result.
- Read your Body fat percentage, to one decimal place, and its Category, then compare it with the body fat categories table.
Putting your result to use
- Work out fat and lean mass. Multiply your weight by the percentage. At 80 kg and 16.4%, fat mass is 80 × 0.164 = 13.1 kg and lean mass is 66.9 kg. Tracking lean mass shows whether weight loss is coming from fat or muscle.
- Read it alongside BMI. The BMI calculator only compares weight with height, so a muscular person can be labeled overweight with low body fat. Body fat percentage fills in what BMI leaves out.
- Measure every two to four weeks. Body fat changes slowly, and daily readings mostly show measurement noise. Measure at the same time of day, ideally in the morning before eating.
- Watch the waist on its own too. A shrinking waist is good news for health whatever the formula says.
Frequently asked questions
How does the Navy body fat calculator work?
It puts your height and neck and waist measurements, plus hips for women, into the U.S. Navy formula, which uses the logarithm of the waist-to-neck difference to estimate the share of your weight that is fat.
How accurate is the U.S. Navy body fat method?
For most adults it is within about 3 to 4 percentage points of laboratory methods such as DEXA. It is less accurate for very lean, very muscular or very heavy people, but it is consistent, which makes it good for tracking change.
Where do I measure my waist for the Navy method?
Men measure at the level of the navel. Women measure at the narrowest point of the waist. Keep the tape level, snug and on bare skin, and do not pull your stomach in.
What is a healthy body fat percentage?
Using the ACE categories, 14–17.9% is the fitness range and 18–24.9% is average for men. For women, 21–24.9% is fitness and 25–31.9% is average. Very low levels, close to essential fat, are not healthy to maintain.
Why do women need a hip measurement?
Women tend to store more fat around the hips and thighs, so the women's formula adds the hip measurement to the waist to capture it. The men's formula uses only the neck and waist.
Can I enter my measurements in inches?
No, the calculator takes centimeters only. Multiply inches by 2.54 to convert: a 15-inch neck is 38.1 cm and a 34-inch waist is 86.4 cm.