The linear dimensions of our sheets are nominal and they have a tolerance of +-1/8" in each direction (length and width). Therefore the dimensions you request will be within the tolerance stated Quality acrylic Weather and scratch resistant Attractive high-gloss finish

SIBE-R PLASTIC SUPPLY 18" x 18" x 3/16" Thick CLEAR Acrylic Plexiglass Plastic Sheet, Better than Glass, for DIY Projects, Transparent Plastic, Signs, Shelves, Design, Display, Cases, Picture