How was the width of the keys on a piano determined?
“In a typical keyboard layout, black note keys have uniform width, and white note keys have uniform width and uniform spacing at the front of the keyboard. In the larger gaps between the black keys, the width of the natural notes C, D and E differ slightly from the width of keys F, G, A and B. This allows close to uniform spacing of 12 keys per octave while maintaining uniformity of 7 natural keys per octave. This scheme has the most uniform distribution, given fixed accidental key width, though not all keyboards are produced this way. 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 125mm to as much as 170mm. Modern piano keyboards ordinarily have an octave span of 164-165mm, but several reduced-size standards have been proposed and marketed, including a 15/16 size (152 mm octave span) and the 7/8 DS Standard (140 mm octave span) developed by Cana
