Body composition calculator
YMCA body fat calculator
Estimate your body-fat percentage from two numbers: your waist and your weight. The YMCA circumference method. Free, instant, no sign-up.
One measurement is a starting point — the coach turns it into a plan and re-checks it as you go.
What is the YMCA body-fat method?
The YMCA equations, from the YMCA's fitness testing and assessment manual, estimate how many pounds of you are fat using only body weight and a single waist measurement at the navel. Divide that fat weight by total weight and you have a body-fat percentage. It is the least equipment-hungry estimate in common use: a tape measure and a scale.
How this calculator works
The equations are written in pounds and inches, so we convert whatever you enter. For men: fat lb = 4.15 × waist − 0.082 × weight − 98.42. For women the intercept changes to 76.76. The modified YMCA equation for men uses 94.42 instead; the modified equation for women is a different shape and needs wrist, hip, and forearm as well, which is why those fields are optional here.
YMCA vs the US Navy method
The two methods disagree on purpose. The Navy method regresses on the log of waist-minus-neck against height, so it accounts for frame size; the YMCA method ignores height entirely and models fat weight directly from waist and body weight. On the same body they can land a few points apart — the Navy method usually tracks better for tall or short people, the YMCA method is quicker to take. If you want the Navy number, run our body fat calculator and compare.
How to use the number
Treat it as a trend line, not a lab result. Measure the waist at the navel, first thing in the morning, relaxed, same tape, same spot — then only compare it against itself. A drift of two points over eight weeks means far more than any single reading. This is an estimate for training decisions, not a medical assessment.