Bike fitting charts suggest frame sizes based on both a person's height and inseam length. To find the correct bike size for one's height, one starts with his inseam length. Inseam length is the distance from one's crotch, where the bike's seat rests, to one's foot.
While a person's torso length and arm's length are important factors to ensure comfortable riding, height and inseam length are the primary measurements used to determine basic bike size. Two formulae discussed with respect to a bike's comfort are stand-over height and top-tube length. Stand-over height equals one's inseam plus an inch or two, to comfortably clear the bike's top tube. One's ideal top-tube length is the distance between a bike's handlebars and its seat at which the rider feels most comfortable.