http://zazzle.custhelp.com/app/answers/detail/a_id/181/~/poster-and-print-sizes-explained
Standard Print Sizes/Dimensions (and minimum resolution requirements)
4″ x 6″ (600 pixels x 900 pixels)
5″ x 7″ (750 pixels x 1050 pixels)
6″ x 6″ (900 pixels x 900 pixels)
8″ x 10″ (1200 pixels x 1500 pixels)
8.5″ x 11″ (1275 pixels x 1650 pixels)
11″ x 14″ (1650 pixels x 2100 pixels)
12″ x 12″ (1800 pixels x 1800 pixels)
12″ x 16″ (1800 pixels x 2400 pixels)
16″ x 20″ (2400 pixels x 3000 pixels)
18″ x 24″ (2700 pixels x 3600 pixels)
19″ x 13″ (2850 pixels x 1950 pixels)
20″ x 24″ (3000 pixels x 3600 pixels)
24″ x 24″ (3600 pixels x 3600 pixels)
12″ x 36″ (1800 pixels x 5400 pixels)
24″ x 36″ (3600 pixels x 5400 pixels)
