Body Fat Percentage Calculator
Estimate your body fat percentage from tape-measure circumferences using the U.S. Navy method — no calipers, no expensive scans.
Body fat — Average
0.19%
- ACE Fitness category
- Average
- Estimated fat mass (kg)
- 14.5
- Estimated lean mass (kg)
- 60.5
The U.S. Navy circumference method (Hodgdon & Beckett, 1984) estimates body fat from tape-measure circumferences and height — no calipers needed. It is an estimate, not a clinical measurement: typical agreement with hydrostatic weighing is within about ±3-4 percentage points for the population it was calibrated on. Not validated for children, pregnancy, or extreme body types. ACE Fitness categories are population-level descriptors, not diagnoses.
How to use this calculator
Pick your sex and unit system, then measure with a soft tape: height, neck just below the larynx, and waist (men: at the navel; women: at the narrowest point above the navel). Women also enter hip circumference at the widest point around the buttocks. Optional weight lets the calculator split the result into estimated fat mass and lean mass. Numbers update instantly as you type.
How the calculation works
The U.S. Navy circumference equations (Hodgdon & Beckett, Naval Health Research Center, 1984) take the log10 of waist-minus-neck (men) or waist-plus-hip-minus-neck (women), and combine it with log10 of height to produce a percentage. For men: 86.010 · log10(waist − neck) − 70.041 · log10(height) + 36.76. For women: 163.205 · log10(waist + hip − neck) − 97.684 · log10(height) − 78.387. All inputs are in inches; metric values are converted with the NIST-exact factor 1 in = 2.54 cm before the formula is applied, so metric and imperial give the same answer.
Worked example
A man who is 70 in tall with a 16 in neck and 35 in waist: waist − neck = 19, log10(19) = 1.27875, log10(70) = 1.84510, so %BF = 86.01 × 1.27875 − 70.041 × 1.84510 + 36.76 ≈ 17.5%. That falls in the ACE Fitness "fitness" band (14–17%) right at the boundary with "average" (18–24%) — reasonable for a recreationally active adult.
Frequently asked questions
How accurate is the US Navy body fat formula?
On the populations it was calibrated against, the Navy circumference method agrees with hydrostatic (underwater) weighing within roughly ±3-4 percentage points for most people. It is an estimate, not a clinical measurement. DEXA, hydrostatic weighing and air-displacement plethysmography are more accurate but require specialist equipment. For tracking change over time the Navy method is plenty precise if you measure consistently.
Where exactly do I measure on my body?
Neck: just below the larynx (Adam's apple), with the tape tilted slightly down at the front. Waist for men: a horizontal line around the abdomen at the level of the navel, after a normal exhalation. Waist for women: the narrowest point of the natural waist, usually above the navel. Hip (women only): the widest horizontal circumference around the buttocks. Keep the tape snug but not compressing the skin.
Why does the formula need height?
Two people with the same waist-minus-neck can have very different body composition if one is much taller — taller frames carry the same circumference over more lean tissue. The log10(height) term in the equation corrects for that, anchoring the percentage to the person's size. Removing it would systematically over-estimate body fat in tall people and under-estimate it in short people.
Is this calculator suitable for children, athletes, or during pregnancy?
No. The Navy equations were derived from adult military personnel and are not validated for under-18s, during pregnancy, or for extremely muscular bodybuilders whose neck-to-waist ratio falls outside the calibration range. Children should be assessed against age- and sex-specific growth charts. Athletes with unusually thick necks may see an artificially low estimate. Pregnant people should not use circumference-based body-fat estimates.
What is a healthy body fat percentage?
ACE Fitness publishes widely-cited descriptive ranges: 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%+. Women carry more essential fat than men because of reproductive physiology. These are population descriptors, not health diagnoses; a clinician will look at trends, distribution, and other markers alongside the number.
Why does my answer differ from a smart-scale or DEXA scan?
Different methods measure different things. Bioelectrical-impedance scales infer body fat from how electrical current passes through tissue, which is sensitive to hydration and meal timing. DEXA uses two X-ray energies to separate fat, lean, and bone — it is the practical gold standard but is not portable. The Navy method estimates from external shape. Expect a few percentage points of disagreement; pick one method and stick with it for tracking change.