Here are a few of the most common sizes based on maximizing your sheet size and budget.
11x17 when displayed on the wall allowing you a 8.5x11 top image, and the days listed as 8.5x11 below.
11x17 or 18x24 poster calendar is 1 sheet of paper with images and all the months
We do offer larger sizes such as 12x24 flat leaving you a top portion of 12x12 and the bottom month being 12x12 however this cost much more due to the size.