How big is a compact car? The size of a "Baby Grand" AKA "Small Grand" is considered by most to be less than 5' 6" in overall length. However, many in the piano industry avoid the term altogether and simply quote the size of the specific model in question. In fact, many piano's model #s have the size embedded in it i.e. "G152" (152 cm = 4'11"). There are no "Standard" sizes of pianos. Every manufacturer can make any piano to her own dimensions. The Bosendorfer Imperial Grand is 290 CM=9'6". David Rubenstein made a grand piano 12' 2". So much for your "Standard Sizes".