Body Fat Calculator

Estimate your body fat with just a tape measure. Enter a few measurements to see your body fat %, your fat and lean mass, and how it compares with study reference ranges for your age and sex.

Your details

years
kg
Sex
cm
cm
cm

Measure with a tape on bare skin, snug but not pressing in. Neck just below the Adam's apple; waist at the navel (men) or the narrowest point (women); hips at the widest point.

Your results

Enter your details and measurements to estimate your body fat.

How to use it

  1. Choose your units, then enter your age, weight, sex and height.
  2. Measure your neck and waist, and for women also your hips. Use a flexible tape on bare skin, snug but not pressing in. Use the tape sites shown in this form, which differ from the midpoint used in the Body Measurement Tracker and Waist to Height Ratio Calculator.
  3. Read your body fat %, fat mass and lean mass.
  4. The table shows study reference ranges for your age and sex. A BMI-based estimate is shown underneath for comparison.

How it's calculated

The Navy formulas. Developed at the Naval Health Research Center (Hodgdon & Beckett, 1984) and later adopted by the US Department of Defense (Hodgdon & Friedl, 1999). All measurements in inches:

  • Men: % body fat = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76
  • Women: % body fat = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387

Centimeters are converted to inches first. The DoD report gives a standard error of about 3.5 percentage points for both formulas.

Fat and lean mass. Fat mass = weight × body fat %. Lean mass is the rest.

Study reference ranges. From Gallagher and colleagues (2000), who linked body fat to BMI cut-offs in adults. The table shows their values for African American and white adults:

Age Men, healthy Women, healthy
20–39 8% to under 20% 21% to under 33%
40–59 11% to under 22% 23% to under 34%
60–79 13% to under 25% 24% to under 36%

The authors proposed these ranges from BMI cutoffs and found differences across groups. The comparison is specific to the study sample. Outside ages 20 to 79, the calculator shows no range.

BMI-based estimate. For comparison only, the Deurenberg formula (1991): % body fat = 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4, where sex is 1 for men and 0 for women. The comparison is limited to adults within the study’s BMI range of 13.9 to 40.9 and age up to 83.

Sources

  1. Hodgdon, J. A., & Beckett, M. B. (1984). Prediction of percent body fat for U.S. Navy men and women from body circumferences and height. Naval Health Research Center, Reports No. 84-11 and 84-29.
  2. Hodgdon, J. A., & Friedl, K. (1999). Development of the DoD body composition estimation equations. Naval Health Research Center, Technical Document No. 99-2B.
  3. Gallagher, D., Heymsfield, S. B., Heo, M., Jebb, S. A., Murgatroyd, P. R., & Sakamoto, Y. (2000). Healthy percentage body fat ranges: an approach for developing guidelines based on body mass index. American Journal of Clinical Nutrition, 72(3), 694–701.
  4. Deurenberg, P., Weststrate, J. A., & Seidell, J. C. (1991). Body mass index as a measure of body fatness: age- and sex-specific prediction formulas. British Journal of Nutrition, 65(2), 105–114.

Questions

How accurate is the Navy method?

In the studies behind the formulas, the typical error was about 3.5 percentage points. The typical error describes the study sample. Individual estimates can differ by more. Measuring carefully, at the same spot each time, matters more than the formula.

What's a healthy body fat percentage?

For adults aged 20 to 39, the ranges used here are 8% to under 20% for men and 21% to under 33% for women. The ranges rise a little with age. They come from a study that matched body fat to healthy BMI values.

Why does it also show a BMI-based estimate?

It's a quick cross-check. BMI-based estimates can't tell muscle from fat, and tape measurements have their own sources of error. A large gap is a reason to recheck your measurements.

Can I track changes with this?

Yes, as long as you measure the same way each time. Small changes of 1 to 2 percentage points can be measurement noise; look at the trend over several weeks. The Body Measurement Tracker can keep your measurements in one place.

Updated November 9, 2026.