CALCULATOR 07
Body Fat Calculator
Estimate body fat % with a tape measure (U.S. Navy method) or from BMI, plus fat and lean mass.
Body fat
Choose the sex used in the formulas.
For general information only; not medical advice. Consult a qualified professional before making health decisions.
How this is calculated
U.S. Navy method (measurements in cm)
Men: %BF = 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450 Women: %BF = 495 ÷ (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450
BMI method (Deurenberg, 1991)
%BF = 1.2 × BMI + 0.23 × age − 10.8 × S − 5.4 (S = 1 men, 0 women)
Composition
Fat mass = weight × %BF ÷ 100 Lean mass = weight − fat mass
ACE categories — men: essential 2–5% · athletes 6–13% · fitness 14–17% · average 18–24% · obese 25%+. Women: essential 10–13% · athletes 14–20% · fitness 21–24% · average 25–31% · obese 32%+.
Sources
- Hodgdon JA, Beckett MB (1984), Prediction of percent body fat for U.S. Navy men and women from body circumferences and height. Naval Health Research Center.
- Deurenberg P et al. (1991), Body mass index as a measure of body fatness: age- and sex-specific prediction formulas. Br J Nutr 65:105–114.
- American Council on Exercise (ACE), body fat percentage categories.
About the body fat calculator
Two ways to estimate
The U.S. Navy method uses a tape measure. Fat around the waist, relative to the neck (and hips for women) and your height, predicts overall body fat surprisingly well. The BMI method, from Deurenberg and colleagues, needs no measuring at all: it estimates body fat from BMI, age and sex. It's quicker but rougher, because it inherits BMI's blind spot for muscle.
Read more about the Body Fat % calculator
How to measure
Use a flexible tape that doesn't stretch. Measure against bare skin, keep the tape level and snug without pressing in, and read it after a normal breath out. Measure the neck just below the larynx (Adam's apple), with the tape sloping slightly down at the front. Men measure the waist at the navel; women at the narrowest point. Women also measure the hips at the widest part of the buttocks. Take each measurement two or three times and use the average.
How accurate it is
For most people, the Navy method lands within a few percentage points of lab methods such as DEXA or underwater weighing, but it can be further off for very lean, very muscular or very heavy people. Measurement technique matters more than anything else—a 1 cm error at the waist shifts the result noticeably. For tracking change over time, consistency beats precision: measure the same way, at the same time of day.
Using your result
The categories from the American Council on Exercise give context, from essential fat to obese. Your fat and lean mass show what your weight is made of. If you save the result to your profile, the BMR calculator can use Katch-McArdle, which bases resting energy on lean mass.
Frequently asked questions
How accurate is the Navy body fat method?
For most people it's within a few percentage points of lab methods, which is good for a tape measure. Careful, consistent measuring matters most.
What is a healthy body fat percentage?
ACE puts average ranges at 18–24% for men and 25–31% for women, with fitness ranges of 14–17% and 21–24%. Essential fat—the minimum for health—is about 2–5% for men and 10–13% for women.
Why does the BMI method give a different number?
It estimates body fat from BMI, which can't tell muscle from fat. It tends to overestimate body fat in muscular people and can underestimate it in people with little muscle. Use the tape method when you can.
How often should I measure my body fat?
Every two to four weeks is plenty. Body fat changes slowly, and measuring more often mostly picks up noise.