Crescent gallery-quality, pre-cut mats have perfectly cut, 45° beveled openings. The cream core bevel, surface, and backing papers, which are buffered and pH neutral, offer excellent protection for your artwork. The fine-quality surface is highly fade-resistant. Mats come shrink-wrapped with an acid-free backing board.
 
The 8" X 8" and 8" X 10" s will have the same size       
Matt Board Frames which is 16" x 20"  and window for picture will be 
7 1/2" X 9 1/2"   
 
The 11" X 14"  will also have a 16" X 20" Matt Board Frame  and window for picture will be  11 1/2" X 15 1/4"