Health & Fitness Calculators

Body composition and energy formulas are estimates built on population averages, and the honest ones say so. BMI was designed in the 1830s to describe populations, not individuals; the Mifflin-St Jeor equation has a standard error of roughly ten percent for any given person; the US Navy body-fat method was designed to be doable with a tape measure on a ship.

Each of these tools names the equation it used, gives the alternatives where they exist, and states the population the equation was fitted to. None of them is a diagnosis, and none of them replaces a conversation with a clinician — but knowing which formula produced a number, and how wide its error bars are, is the difference between a useful estimate and a number to worry about.