UNDERSTAND THE METHOD
How to use this calculator
Enter height, weight, and a body-fat percentage from a stated measurement method. FFMI divides fat-free mass by height squared. The height adjustment uses 1.80 m as its reference. Select a convention before comparing results from different calculators.
What the result can tell you
Fat-free mass includes water, organs, and bone as well as muscle. The original sample contained male athletes. Its observations do not establish an individual natural limit or prove drug use. A body-fat input error changes every derived result.
Common questions
Why can I choose a 6.3 or 6.1 height adjustment?
The original abstract reports 6.3, while 6.1 is a common calculator convention. Choose one convention before comparing FFMI results.
Does FFMI measure muscle or establish a natural limit?
No. Fat-free mass also includes water, organs, and bone. The source observations do not establish an individual natural limit or prove drug use.
Sources & limitations1 source
Sources checked September 12, 2026. These notes identify methods and assumptions. They have not received an independent clinical review.