Body Fat Calculator (U.S. Navy Method)

This body fat calculator estimates your body fat percentage from a few tape measurements, using the U.S. Navy method. Enter your height, waist and neck (and hips for women). The result is an estimate that can be several percent off, so use it to follow your own trend over time, not as an exact number.

Body fat calculator

This calculator needs JavaScript. The formulas are explained below.

Body fat percentage matters a lot in fitness. A lean, muscular look comes from having good muscle mass and a relatively low body fat percentage. The problem is that body fat is not easy to measure. Two people who both weigh 80 kg can look completely different if one has 10% body fat and the other has 25%. That is why your weight alone does not tell you much.

What is body fat percentage?

Body fat percentage is the share of your total body weight that is fat tissue. Some fat is essential for health. Both very high and very low body fat are linked to health risks, which is one reason it helps to know roughly where you are. Tracking it also shows you whether a fat-loss or muscle-gain phase is working, even when the scale barely moves.

How the calculator works

The calculator uses the U.S. Navy circumference method, developed at the Naval Health Research Center. It is one of the most widely used tape-measure methods. It needs:

• Sex: the equations for men and women are different.
• Height.
• Neck: measured just below the Adam's apple (larynx).
• Waist: for men, around the belly at the level of the navel; for women, at the narrowest point.
• Hips (women only): at the widest point of the buttocks.
• Weight (optional): if you add it, the calculator also shows your estimated fat mass and lean mass.

The formulas behind the calculator

Measurements are in centimeters, and log is the base-10 logarithm:

• Men: body fat % = 495 / (1.0324 − 0.19077 × log(waist − neck) + 0.15456 × log(height)) − 450
• Women: body fat % = 495 / (1.29579 − 0.35004 × log(waist + hips − neck) + 0.22100 × log(height)) − 450

If you enter inches, the calculator converts them to centimeters first.

How accurate is it?

No formula can measure body fat exactly, because it cannot see how much muscle you have or where your body stores fat. In a study of 31 young white college men, the military tape-measure equations, including the Navy one, had a total error of about 5 percentage points against a laboratory reference, which the authors judged too large. A Navy validation study in people with high body fat (men 22% or more, women 30% or more) found the method less reliable in that group, and the authors advised caution when using it for decisions about one person.

For most people, the estimate is good enough to follow a trend: measure the same way, and watch whether the number goes up or down.

There are more accurate options, such as a DEXA scan, hydrostatic (underwater) weighing and air-displacement devices (Bod Pod). They usually cost money and are found in labs and clinics. Bioelectrical impedance scales are cheaper, but their accuracy depends a lot on the device and on how hydrated you are.

Body fat percentage chart

Here are the body fat ranges widely attributed to the American Council on Exercise (ACE) for men and women; ACE's own site confirms the average ranges and the too-low limits. They are general guidelines, and can vary between people with fitness level, genetics and lifestyle. After you use the calculator, compare your result with the chart.

As you can see, women usually have a higher body fat percentage, stored more around the hips and thighs. This is a normal biological difference. Estrogen, a hormone women naturally have more of, plays a part in how and where fat is stored. Men tend to store more fat around the belly, which is linked partly to testosterone.

A body fat percentage under the "athletes" range (below about 14% for women or 6% for men) may be too low for health. Do not use the chart as a target to get as low as possible.

Tips for a more accurate measurement

• Measure in the morning. The amount of fluid in your body changes during the day. That can change your weight and make your belly look and measure bigger.
• Watch the units. Choose centimeters or inches in the calculator and use the same unit for every measurement. A height of 1.75 m is 175 cm.
• Use a flexible tape measure. Keep it level and snug on the skin, without pressing into it. Measure each site two or three times and use the average.
• Measure relaxed. Stand straight, breathe out normally, and do not pull your belly in.
• Keep a tracking list. Write down the date, your weight and your body fat estimate. It helps you see if you are moving forward or standing still.

Bottom line

A body fat calculator gives you an estimate of how much fat your body carries. Once you know roughly where you are, you can decide what your next goal is. If you want to lower your body fat, a steady approach works better than a fast one. You can also talk to a qualified professional: a good coach or a registered dietitian can save you a lot of mistakes. If you have a medical condition, talk to your doctor first.

Frequently asked questions

How accurate is the Navy body fat calculator?

It is an estimate. Studies found errors of a few percentage points, and more error for people with very high body fat. It works best for tracking your own changes over time.

Why do women need a hip measurement?

The Navy equation for women uses the waist, hips and neck, because women store more fat around the hips.

How often should I measure?

Every two to four weeks is enough. Body fat changes slowly, and daily measurements mostly show normal ups and downs.

What is a healthy body fat percentage?

The ACE chart above gives general ranges. What is healthy for you also depends on your age, health and goals, so ask a healthcare professional if you are unsure.