This depends on what print medium you are using. Paper comes in a number of standard sizes:
Paper Size Dimension (in points)
------------------------------ ---------------------
Comm #10 Envelope 297 x 684
C5 Envelope 461 x 648
DL Envelope 312 x 624
Folio 595 x 935
Executive 522 x 756
Letter 612 x 792
Legal 612 x 1008
Ledger 1224 x 792
Tabloid 792 x 1224
A0 2384 x 3370
A1 1684 x 2384
A2 1191 x 1684
A3 842 x 1191
A4 595 x 842
A5 420 x 595
A6 297 x 420
A7 210 x 297
A8 148 x 210
A9 105 x 148
B0 2920 x 4127
B1 2064 x 2920
B2 1460 x 2064
B3 1032 x 1460
B4 729 x 1032
B5 516 x 729
B6 363 x 516
B7 258 x 363
B8 181 x 258
B9 127 x 181
B10 91 x 127
To determine what print mediums are available, check the PPD file for your printer, under the PageSize keyword.