Why? I think the long sides are the paper roll widths and then it is cut to length. I guess 15 is not a paper width and neither is 6. But you do have 8x12. Everything is in the ratio you upload.
The sizes depend on your pixels. Unlike other sites we never crop or skew images to fit standard sizes, instead allowing the artist free scope to just upload what they have
The only limits we have are that one of your dimensions is going to be forced to fit the following list:
8"
10"
12"
14"
16"
20"
24"
32"
36"
48"
The other dimension will be scaled proportionally to maintain the aspect ratio of your image. (Up to a maximum of 108")
