●Outer measurements - to fit an A4 frame. Exact mount size 297mm x 210mm. ●Inside measurements - to fit an A5 image. Exact aperture size 203mm x 140mm. ●Our mounts and backing boards are cut from conservation grade whitecore mountboard, 1.4mm thick, acid free. Square cut outer edges, bevelled cut on the inner edges. ●This is a pack of 10 sets - 10 mounts, 10 backs, and 10 resealable cellophane bags. ●For other picture sizes and colours please select from the options menus.