FAA size chart: Print Size vs Pixel Size

One side of your image must be at least this many pixels in length or more (your images pixels x pixels show in bold above the price chart after you upload your image). If the image just barely makes the requirement, I suggest dropping one size down just to be on the safe side. If the pixels sizes land in between, choose the lesser of the two:

8 x 0 = 686 (pixels)
10 x 0 = 857
12 x 0 = 1229
14 x 0 = 1200
16 x 0 = 1371
20 x 0 = 1714
24 x 0 = 2055
30 x 0 = 2571
36 x 0 = 3086
40 x 0 = 3429
48 x 0 = 4114
60 x 0 = 5143
72 x 0 = 6171
96 x 0 = 8229
108 x 0 = 9257

Use the pixel chart for both sides. Height and width.

Remember, if your images are blurry or pixelated they still will not be printable. Probably at any or most of the sizes you offer. It must be sharp at the required pixels. The photo cannot be enlarged to fit. Clean, sharp photos straight from the camera or scanner is best. If you do some processing, take the biggest one or two sizes you can offer off by leaving the price box empty. Especially if it barely fits into the required pixels by pixels.