We are gradually providing detailed sizing information on all our listings but the following general rules apply.
Stated frame sizes refer to the picture size for which the frame is suitable.
Overall frame sizes are measured at the widest/longest parts of the frame.
Opening sizes, where referred to, are the dimensions of the frame measured from the front; these are smaller than the stated frame size since they allow for the frame rebate. In general they are around 3/8"-1/2" (9mm-12mm smaller than the frame size.