Those are the "product dimensions" for which they also give a depth (the first hint that the dimensions given are not keyed to the glass size). You'll find this is the size of the outside of the frame, which is quite useful to know if you are a decorator (the intended market). The size of the glass will be smaller and this dimension is not disclosed. If you are buying an empty frame, the dimensions given are a nominal width and height with generally 1/8" extra room in each dimension (to allow for 1/16" space all around). But if you are buying a decor item, the dimensions given are generally the overall size.