19.25 cm using the OP measure. Funnily, I can only reach a tenth.

Oh and Rachmaninoff_forever, you need more than two octaves for some Brahms chords, so you're still gonna have to roll.

Incidentally, given that he marked both that the chords were to be rolled, and that pedal had to be used, Alkan obviously had some VERY strange hands in mind for the player of these chords (from Sonate pour les quatres ages), who he appears to have though might have avoided either.

