About this tool
The FFMI Calculator turns your weight, height and body-fat percentage into a Fat-Free Mass Index — a way to gauge how much muscle you carry relative to your height, independent of body fat. Everything is computed live in your browser and nothing is uploaded.
First your lean body mass is found as LBM = weight × (1 − body-fat% ÷ 100). FFMI is then LBM in kilograms divided by your height in metres squared (FFMI = LBM ÷ height²). Because taller people tend to score lower, a height-normalized FFMI is also shown as FFMI + 6.1 × (1.8 − height in metres), which adjusts every result to a 1.8 m reference height. The classification band (below average, average, above average, excellent, superior, or suspiciously high) is read from the normalized value.
This is general educational information, not medical advice. FFMI is a rough index built from a formula, not a body-composition scan, and a very high score does not by itself prove anything — use it as a fitness reference and speak with a qualified professional for real guidance.