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CalculatorsBody Composition

Body Fat Calculator

This body fat calculator estimates your body fat percentage from a tape measure and the Navy method.

Your numbers

Sex used in the formula

These formulas come in a male and a female version. Pick the one that fits best.

Measure just below the Adam's apple, with the tape level and snug.

Men: at the navel. Women: at the narrowest part of the waist. Stand relaxed and breathe out.

Add it to see your fat mass and lean mass.

Where to go next

Field Notes that go deeper

The science behind the body fat calculator

Show the formulas, method and sources

The Navy method estimates body fat from tape measurements and height. It needs only a tape measure, so it works at home. It is still an estimate, and it can sit several percentage points away from a scan.

Formulas

Men (measurements in cm)

  • Body fat % = 86.010 x log10((abdomen - neck) / 2.54) - 70.041 x log10(height / 2.54) + 36.76

Women (measurements in cm)

  • Body fat % = 163.205 x log10((waist + hip - neck) / 2.54) - 97.684 x log10(height / 2.54) - 78.387

Fat and lean mass (when you enter your weight)

  • Fat mass = weight x body fat % / 100
  • Lean mass = weight - fat mass

How it works, step by step

  1. First, the calculator converts your measurements to centimeters and divides by 2.54, so the equation works in inches.
  2. Then it applies the equation for your sex. The women's version also uses the hip.
  3. If the logarithm cannot be calculated, for example when the neck is as wide as the waist, it asks you to re-measure.
  4. Finally, it rounds the result to one decimal place.

Worked example

A man who is 180 cm tall, with a 38 cm neck and an 85 cm abdomen, gets about 16.2% body fat. A woman who is 165 cm tall, with a 32 cm neck, a 75 cm waist and a 98 cm hip, gets about 29.2%.

Accuracy and limits

A 2023 study in Frontiers in Physiology compared the Navy and Army circumference equations with DXA scans in military trainees. The standard error came to about 3.3 to 4.1 percentage points, depending on sex and timing.

The tape method also read lower than DXA by 2 to 6 percentage points on average in that group. Because trainees differ from the general public, your gap could be different.

The same study found that the tape method did not capture changes in body composition well during training. If you track progress, compare tape results with each other, and measure the same way each time.

  • This is a screening estimate, not a diagnosis. It also cannot tell you where your fat sits or how healthy you are.
  • Tape position, posture and breathing change the numbers, so a one-centimeter slip at the waist moves the result.
  • Because healthy ranges depend on age, sex and goals, the result carries no good or bad label. A clinician can place your number in context.

Sources

  1. Foulis SA, Friedl KE, Spiering BA, et al. Body composition changes during 8 weeks of military training are not accurately captured by circumference-based assessments. Front Physiol. 2023;14:1183836. Used for: The Navy and Army circumference equations as written, and their error against DXA scans in one group.

Sources and math last reviewed: .

Questions people ask

How do I take the measurements for the Navy method?

Use a flexible tape, snug but not squeezing the skin. Measure the neck below the Adam's apple. For the waist, men measure at the navel and women measure at the narrowest part. Women also measure the hips at the widest point. Stand relaxed, then measure twice and use the average.

How accurate is the Navy body fat method?

It gives a rough estimate. One 2023 study of military trainees found a standard error of about 3 to 4 percentage points against DXA scans, and the tape method read lower on average. Expect your result to land near the real value, with some error either way.

What is the difference between body fat and BMI?

BMI compares weight with height, so it cannot tell fat from muscle or bone. A body fat estimate tries to show the fat share of your weight. The two can disagree, so using both gives a fuller picture.

Is there a healthy body fat percentage?

Ranges depend on age, sex and your goals, and published charts do not agree with each other. That is why this calculator shows your number without a label. A clinician or dietitian can read it alongside your other health information.

How often should I re-measure?

Once every few weeks is plenty, because day-to-day changes in water and food can shift a tape reading more than a real change in fat. If you measure at the same time of day and in the same way, you can compare trends.

These calculators give general estimates for adults and are not medical advice. For decisions about your own health, talk with a doctor or a registered dietitian. How we write and check things