ISO 216 paper sizes while you're at it, please!
The 'A' system for paper has many advantages, and actually would be something that could be accessibly changed (all printers and scanners handle it just fine).
The ISO system in general, ISO 216 and 269 provide 3 series (A, B and C, A is the base series, B is the geometric mean between two sizes of the A series, C is the geometric mean between the A and B series at a given index, and is thus mostly used for envelopes for the A series: an envelope Cn will hold an An sheet without folding, and of course a Cn envelope will fit an A(n-1) folded in two)