http://en.wikipedia.org/wiki/Musical_keyboard

itt többféle "szabványos" méretről is regél:

"Over the last three hundred years, the octave span distance found on historical keyboard instruments (organs, virginals, clavichords, harpsichords, and pianos) has ranged from as little as 125 mm to as much as 170 mm. Modern piano keyboards ordinarily have an octave span of 164–165 mm; resulting in the width of black keys averaging 13.7 mm and white keys about 23.5 mm wide at the base, disregarding space between keys. Several reduced-size standards have been proposed and marketed. A 15/16 size (152 mm octave span) and the 7/8 DS Standard (140 mm octave span) keyboard developed by Christopher Donison in the 1970s and developed and marketed by Steinbuhler & Company. U.S. pianist Hannah Reiman has promoted piano keyboards with narrower octave spans and has a U.S. patent on the apparatus and methods for modifying existing pianos to provide interchangeable keyboards of different sizes.[2] "