My primary camera is a 3:2 aspect ratio, the same as a 35mm film camera (24x36mm).
I usually compose my images using the full frame, so cropping will cut out some subject matter. This format yields full frame prints that are 4x6, 8x12, 24x36, etc., without cropping the original image. An image that is printed to 8x10 will lose about 17% of the image on the long side. An 8x12 can be reduced to 10 inches on the long side, but in order to keep the same aspect ratio, the short side will be reduced to just over 6.5 inches instead of 8 inches. A 5x7 with a 3:2 aspect ratio, un-cropped, will be about 4.6 inches on the short side to use the full frame at 7 inches on the long side.

Sometimes a landscape shot may be compressed or stretched to accommodate a different aspect ratio with the distortion of the original image not being objectionable. However, this does not work well if people or certain other objects are in the picture, as those objects will be depicted as wider or taller than normal.

Pre-cut 11x14 mats for an 8x12 print are available, but a mat for a 6.5x10 print will most likely need to be custom cut, as would a 4.6x7.