Estimate your body fat with the U.S. Navy tape-measure method. All you need is a tape measure.
Tape-measure estimates are usually within 1-3% of a DEXA scan when you measure the same way each time.
A body fat percentage calculator estimates how much of your weight is fat versus lean tissue using the U.S. Navy tape-measure formula from 1984. Enter your height, neck, waist, and (for women) hip measurements in inches, and it returns your estimated body fat percentage in seconds.
How the Calculator Works
The U.S. Navy method was developed by Hodgdon and Beckett at the Naval Health Research Center in 1984 as a practical way to estimate body composition without lab equipment. It uses logarithms of a few circumference measurements to predict body density, then converts the result into a body fat percentage.
For men, the formula uses height, neck, and waist: BF% = 86.010 x log10(waist - neck) - 70.041 x log10(height) + 36.76. For women, it adds a hip measurement: BF% = 163.205 x log10(waist + hip - neck) - 97.684 x log10(height) - 78.387. All measurements are in inches.
The calculator applies the correct formula for your sex and rounds the answer to one decimal place. The key inputs are the waist-to-neck gap for men and the waist-plus-hip-minus-neck total for women.
How to Use This Calculator
- Measure your height in inches. Stand straight against a wall without shoes and mark the top of your head, then measure down to the floor.
- Measure your neck just below the larynx, the bump often called the Adam's apple. Keep the tape snug but not tight, and look straight ahead.
- Measure your waist. Men measure at the navel. Women measure at the narrowest point of the midsection, usually just above the navel.
- Women also measure the hips at the widest point around the buttocks, keeping the feet together.
- Enter each measurement in inches, select your sex, and read your estimated body fat percentage.
- Re-measure every two to four weeks under the same conditions, the same time of day and the same tape tension, so you track real change instead of noise.
Verified Worked Examples
The table below shows two complete calculations. Intermediate steps are rounded for readability, and the final answers match the calculator to one decimal place.
| Person | Measurements (inches) | Key steps | Result |
|---|---|---|---|
| Man | Height 70, neck 15, waist 34 | log10(34 - 15) = log10(19) = 1.2788, so 86.010 x 1.2788 = 109.99. log10(70) = 1.8451, so 70.041 x 1.8451 = 129.23. | 109.99 - 129.23 + 36.76 = 17.5% (17.52 unrounded) |
| Woman | Height 64, neck 13, waist 28, hip 38 | log10(28 + 38 - 13) = log10(53) = 1.7243, so 163.205 x 1.7243 = 281.41. log10(64) = 1.8062, so 97.684 x 1.8062 = 176.43. | 281.41 - 176.43 - 78.387 = 26.6% (26.59 unrounded) |
You can turn a percentage into pounds. Fat mass equals body weight times body fat percentage divided by 100, and lean mass equals total weight minus fat mass. For example, a 180-pound person at 17.5% body fat carries 31.5 pounds of fat (180 x 0.175 = 31.5) and 148.5 pounds of lean mass (180 - 31.5 = 148.5).
What Your Result Means
The American Council on Exercise (ACE) publishes the most widely used body fat categories. Find your band in the table below.
| 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% and above | 32% and above |
Most healthy adults land in the fitness or average bands. Values in the obese band are worth discussing with a doctor, and values at or below essential fat can be unhealthy if held for long.
How Accurate Is the Navy Method?
When measurements are taken carefully and consistently, the Navy method usually lands within about 1 to 3 percent of a DEXA scan result, and it is often quoted with a margin of plus or minus 3 to 4 percent. That makes it one of the most accurate methods you can use at home, far better than estimating from the mirror.
Accuracy drops when the tape is pulled tight, when you measure at a different spot each time, or for very muscular people, for whom the formula can overestimate. Pregnant women should not use it. Consistency matters more than perfection: measure the same way every time and watch the trend over weeks.
Why Body Fat Percentage Beats the Scale
Two people can weigh the same and carry very different amounts of fat. A 180-pound athlete at 12% body fat carries about 21.6 pounds of fat (180 x 0.12 = 21.6), while a 180-pound sedentary person at 28% carries about 50.4 pounds (180 x 0.28 = 50.4). The scale cannot tell them apart, but body fat percentage can.
Tracking the percentage also keeps weight loss honest. If the scale drops but your body fat percentage stays flat, you may be losing muscle instead of fat, which is a sign to eat more protein and add strength training.
Frequently Asked Questions
Do I need calipers or a smart scale to use this calculator?
No. A flexible tape measure is the only tool you need. The Navy formula was designed for tape measurements, which is why it works well at home with no special equipment.
Do men and women use the same formula?
No. Men use height, neck, and waist, while women add a hip measurement. The two formulas have different constants because men and women store fat in different places.
How often should I measure my body fat?
Every two to four weeks is ideal, always at the same time of day. Body fat changes slowly, so weekly checks mostly show water shifts and measurement noise.
Is the Navy method accurate for very muscular people?
It can overestimate body fat in people with a lot of muscle, because a thick neck or waist built from muscle looks like fat to the formula. Athletes may want calipers or a DEXA scan as a second opinion.
Can I use this calculator while pregnant?
No. The formula was not developed or validated for pregnancy, and changing body shape makes the result meaningless. Wait until after recovery to resume tracking.
What is a good body fat percentage goal?
For most men, the fitness band of 14-17% is a solid target, and for most women, 21-24% works well. Goals below the athlete band are hard to maintain and can affect hormones and energy, so aim for a range you can hold year-round.
Learn More
These guides go deeper into every part of measuring and managing body fat: