This tool is supposed to help in calculating fat free mass. Apparently it indicates if someone is outside of the range that can be attained naturally there is a lot of people singing its praises.
https://www.thecalculator.co/health/Fat-Free-Mass-Index-(FFMI)-Calculator-794.html
https://www.thecalculator.co/health/Fat-Free-Mass-Index-(FFMI)-Calculator-794.html