A worked example
A male at 180 lb and 5'10" has an estimated lean body mass of about 135.6 lb — meaning roughly 44.4 lb, or about 25% of total weight, is estimated as fat mass.
Frequently asked questions
What counts as 'lean body mass'?
Everything that isn't fat — muscle, bone, organs, water, connective tissue. It's a broader category than just muscle mass, even though the two are often used loosely interchangeably in casual conversation.
How accurate is a formula-based estimate versus a body fat test?
A direct body fat measurement (DEXA scan, hydrostatic weighing, or even a reasonably careful circumference method) will be more accurate for any one individual, since this formula is fitted to population averages rather than your specific body composition.
This calculator provides estimates for general informational purposes only and is not medical advice.