Body Fat Percentage: What It Means and How to Measure It
Body fat percentage is the proportion of your total body weight that is composed of fat tissue. Unlike BMI, which only uses height and weight, body fat percentage distinguishes between fat mass and lean mass (muscle, bone, organs, and water). This makes it a more informative health metric, particularly for athletes who may have a high BMI due to muscle but very low body fat, and for older adults who may have a normal BMI but a disproportionately high fat percentage.
The US Navy Method
The US Navy circumference method was developed as a practical field measurement that correlates well with underwater weighing (hydrostatic density testing), which is considered a gold standard for body fat measurement. For men, the formula is: BF% = 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76. For women: BF% = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387. All measurements are in centimeters. The method is accurate to within about 3–4% for most individuals.
How to Take Measurements
Accuracy depends on taking measurements correctly. For the waist, measure at the level of your navel (belly button), keeping the tape horizontal and not compressing the skin. For the neck, measure just below the larynx (Adam's apple), with the tape slightly angled downward at the front. For women, the hip measurement is taken at the largest circumference of the hips and buttocks. Measure twice and average the values for best accuracy.
Body Fat Categories
The American Council on Exercise (ACE) defines body fat categories as follows. For men: essential fat 2–5%, athletes 6–13%, fitness 14–17%, acceptable 18–24%, obese 25%+. For women: essential fat 10–13%, athletes 14–20%, fitness 21–24%, acceptable 25–31%, obese 32%+. Women carry more essential fat due to hormonal and reproductive physiology, so the categories are naturally higher. These are guidelines, not strict clinical cutoffs.
Body Fat vs BMI
BMI is a faster and simpler calculation but misses body composition. A well-muscled athlete with very low body fat may have a BMI of 27 (overweight category) because muscle is denser than fat. Conversely, a sedentary person with a normal BMI of 23 may have 28% body fat (acceptable-to-high range) due to muscle loss over time — a phenomenon sometimes called "skinny fat" or normal-weight obesity. For most people, using BMI and body fat percentage together gives a much better picture of health than either alone.
This calculator is for general estimates only and is not medical advice. Body fat estimates can vary by ±3–4% from more precise laboratory methods.