How the US Navy body fat method works
The US Navy method estimates your body fat percentage from a few tape measure readings and your height. It was developed for the US Navy in the 1980s as a quick field test, and the military still uses it. Fat around the waist makes the waist grow faster than the neck, so the gap between the two says a lot about how much fat you carry. For women the formula also uses the hip, where many women store more fat.
No calipers, scale or lab needed: a flexible tape measure is enough. That makes this body fat calculator a handy way to follow your progress at home.
The formulas
These are the published formulas with every measurement in inches. In metric mode, the calculator divides your centimeters by 2.54 first. log10 is the base 10 logarithm.
Lean mass = Weight − Fat mass
Example: a man 5 ft 10 in (70 in) tall with a 15 in neck and a 34 in waist gets 86.010 × log10(19) − 70.041 × log10(70) + 36.76, which is about 17.5% body fat. At 180 lb that is about 31.5 lb of fat mass and 148.5 lb of lean mass, which includes muscle, bone, organs and water.
How to measure: where to put the tape
Small measuring errors move the result a lot, especially at the neck. Use a flexible, non-stretch tape, stand relaxed and upright, and keep the tape snug against the skin without pressing in. Measure each spot two or three times and use the average, ideally at the same time of day, for example in the morning before eating.
- Neck: just below the larynx (Adam's apple), with the tape sloping slightly down toward the front. Look straight ahead and do not flare your neck.
- Waist, men: horizontally around the belly at the level of the navel, after breathing out normally. Do not suck in.
- Waist, women: at the natural waist, the narrowest point between the lower ribs and the top of the hips, after breathing out normally.
- Hip, women: around the widest part of the hips and buttocks, feet together, tape level all the way around.
- Height: without shoes, standing straight against a wall.
Body fat percentage categories
| Category | Men | Women |
|---|---|---|
| Essential fat | 2 to 5.9% | 10 to 13.9% |
| Athletes | 6 to 13.9% | 14 to 20.9% |
| Fitness | 14 to 17.9% | 21 to 24.9% |
| Average | 18 to 24.9% | 25 to 31.9% |
| Obese | 25% and up | 32% and up |
These ranges are commonly published by the American Council on Exercise (ACE). Essential fat is the minimum your body needs to work normally, and women need more of it than men. The categories are a rough guide: what is healthy for you also depends on your age, your health and where on your body the fat sits.
How accurate is it?
For many adults the Navy formula comes within a few percentage points of lab methods, which is about as good as tape measure estimates get. It tends to be less accurate for very lean people, bodybuilders with a thick neck, and people with an unusual fat distribution. A single number is less useful than the trend: measure the same way every two to four weeks and watch which way it moves. This page is for information, not medical advice. If you need an exact figure, ask about a DEXA scan or another clinical method.
How to use the body fat calculator
- 1Pick US or metric units and your sex, then enter your height.
- 2Measure your neck and waist, and for women also your hips, as described above, and enter the averages.
- 3Add your weight to see fat mass and lean mass, then read your body fat percentage and category.
Frequently asked questions
How accurate is the US Navy body fat method?
For many adults it lands within a few percentage points of lab methods such as DEXA scans, which is good for a tape measure. It can be further off for very lean or very muscular people, and for people who store fat mostly on the hips, thighs or belly. Careful, repeated measurements matter more than the formula. Use the trend over weeks rather than a single reading.
What is a healthy body fat percentage?
Commonly published ranges from the American Council on Exercise put fitness level at 14 to 17% for men and 21 to 24% for women, and average at 18 to 24% for men and 25 to 31% for women. Men need at least about 2 to 5% and women about 10 to 13% essential fat for normal body function. Age, genetics and health history all play a role, so talk to a doctor for a personal target.
Why does the formula for women need a hip measurement?
Women tend to store more fat around the hips and thighs than men, so a waist and neck measurement alone would miss a large part of it. The women's formula adds the hip circumference to the waist and subtracts the neck. Men's fat sits more around the belly, so waist minus neck is enough.
Where exactly should I measure my waist?
For the Navy method, men measure around the belly at the level of the navel. Women measure at the natural waist, the narrowest point between the lower ribs and the hips. Stand straight, breathe out normally and keep the tape level and snug without pressing into the skin.
What is the difference between body fat and BMI?
BMI only compares weight with height, so it cannot tell fat from muscle. A muscular person can have a high BMI with low body fat. Body fat percentage looks at how much of your weight is fat, which is closer to what most people actually want to know. Both are rough screening tools, not a diagnosis.