Standard Print Sizes:
Business Card Size: 3.5×2
Half-Letter: 5.5×8.5 (Books, fliers, etc.)
Letter: 8.5×11 A very standard size. (Letters, Newsletters, Small Posters, Books, etc.)
Tabloid: 11×17 (Posters, Saddle Stitched Booklets (Stapled and folded), etc.)
Oversized Tabloid: 12×18 (Posters with bleed, or just larger posters.)
Envelopes:
#9 Envelope: 3.875×7.5 (Frequently used for business reply mail envelopes.)
#10 Envelope: 4.125×9.5 (This is a standard business sized envelope.)