i actually wash and dry everything as it arrives home. then i fold selvedge to selvedge and selvedges to fold, all the way down the length. then i accordian fold at between 8 - 9" (eyeballed). i can usually tell at a glance approximately what i have. if anything, i tend to underestimate, which is fine with me. the scrappy stash grows. i do this with all my quilt fabrics, but not my garment fabrics. the garment fabrics often are too slidey to stay well-folded. they often end up in plastic zip bags or in a lump. i just have to measure them when needed. often i work the other way around. how much do i have and what can i use it for? i buy on spec.
also, i separate my quilt fabric by color, but i don't separate garment fabric at all. i know exactly where every piece is, as hard as that is to believe.