Body Fat Calculator

Why body fat percentage beats BMI

BMI can't tell the difference between a kilogram of muscle and a kilogram of fat, which is why two people with an identical BMI can look and function very differently. Body fat percentage answers a more useful question: of your total body weight, how much is fat mass versus lean mass (muscle, bone, organs and water)? This calculator uses the U.S. Navy circumference method, a validated approach that only needs a flexible tape measure rather than expensive equipment like DEXA scans or skinfold calipers.

How the U.S. Navy method works

The formula was developed for military fitness assessments and relies on your height plus circumference measurements at the neck and waist (with hips added for women). It uses logarithms of these measurements because body fat doesn't scale in a straight line with girth — a small change in waist circumference can represent a larger swing in body fat percentage than the same change in neck circumference. Measure directly against skin rather than over clothing, keep the tape snug but not compressed, and measure at the same time of day for consistency if you're tracking change over weeks.

Reading your body fat category

Essential fat is the minimum your body needs to function and sits around 2–5% for men and 10–13% for women. Athletic ranges typically run 6–14% for men and 14–21% for women, while 'average' ranges extend up to roughly 25% and 32% respectively before crossing into higher-risk territory. These bands come from widely cited fitness references such as the American Council on Exercise, and like BMI, they're guidelines rather than a diagnosis.

Getting a more accurate picture

Tape-measure methods are convenient but carry a margin of error of a few percentage points compared to lab methods like hydrostatic weighing or DEXA scans. For most people tracking general fitness progress, that's more than accurate enough — what matters most is the trend over time rather than the exact number on any single day. Re-measuring every 4–6 weeks under similar conditions will give you a far more reliable signal than obsessing over daily fluctuations.