The registers have dimensions 6.25" x 12.5". The frames have dimensions 8.375" x 14.5".
I have 3 registers here. One of them has what I think is water damage. The damage is only on the back so it won't affect the look when it's installed (see photos). Another one has a small notch on one corner of the frame that could be sanded down or ripped before installing (see photos).