What is a body fat calculator?
A body fat calculator estimates the proportion of total body weight that is fat mass. Unlike the height-to-weight relationship used by the BMI calculator, this page uses circumference-based equations developed for U.S. Navy personnel.
The remaining body weight is shown as estimated lean mass. Lean mass includes muscle, bone, organs, connective tissue, and body water; it is not the same as muscle mass.
How does the body fat calculator work?
The tool converts metric measurements to inches, checks that each circumference is plausible for the equation, and applies the sex-specific U.S. Navy logarithmic formula. It then uses body weight to estimate fat mass and lean mass.
Small tape-placement or tension differences can noticeably affect the result. Measure under similar conditions and consider averaging two or three careful readings.
U.S. Navy body fat formulas
Male equation
Female equation
The direct percentage equations shown here use inches. Metric entries are converted before calculation. These equations were developed from military samples and may not generalize equally to every population.
How to measure correctly
- Height: Stand upright without shoes.
- Neck: Keep the tape level below the larynx without squeezing.
- Male waist: Measure the abdomen at the navel after a normal exhale.
- Female waist: Measure the natural waist at its narrowest point.
- Female hip: Measure around the widest part of the hips and buttocks.
Use the same tape and protocol when comparing results over time.
Understanding the result
The large number is estimated body fat as a percentage of total body weight. The reference label uses broad adult fitness categories and should not be treated as a clinical threshold.
Fat mass and lean mass are mathematical splits of the entered weight. If you are planning nutrition from body weight, the protein calculator provides a separate evidence-informed intake range; it does not use this body-fat estimate.
Limitations and appropriate use
Circumference estimates can differ from DEXA, air-displacement plethysmography, underwater weighing, and properly performed skinfold testing. Hydration, anatomy, age, ethnicity, muscularity, recent exercise, and tape technique can affect comparisons.
This calculator is not intended for pregnancy, anyone under 18, or clinical decisions. A qualified health professional can select a suitable assessment method when accuracy matters.
Frequently asked questions about body fat
Sources and methodology
The method and interpretation are documented with research and U.S. health resources.