All prints have a white border so:

An 8 x 6" (20.3 x 15.2cm) print has an actual picture size of 7 3/4 x 5 3/16" (19.7 x 13.2cm) and comes in a 10 x 8" (25.4 x 20.3cm) mount.

A 12 x 8" (30.45 x 20.3cm) print has an actual picture size of 10 1/2 x 7" (26.6