12"w X 18"h Is The Size For The Duct Opening Measurement Only, Actual Front End Outer Dimensions Are 13.85" Width X 19.85" Height - SEE BELOW IN DESCRIPTION HOW TO MEASURE A GRILLEHVAC Premium has been providing superior in quality service for many many years. Our products are second to none, and we ve helped numerous contractors, DIY projects, and home improvement remodeling specialists complete their masterpiece. If you are looking for a top of the line unit to enhance your project look no further than HVAC Premium. We have the largest selection of Grilles Registers & Diffusers. HVAC Premium has sold over 5,000,000 Grilles - We are proud of our many happy customers! Never Rust - Our high quality rigid aluminum is the longest lasting filter grille on the market. It will never rust,and will be easy to clean. The rigid Aluminum will keep its shape as in brand new condition. Elegance - Beautifully Structured To Add A Touch Of Upper Class To You Room And HVAC system. Quality Packaging - Carefully Shrink Wrapped With Cardboard Backing To Prevent Damage In Shipment How To Measure A Grille Overall Size: Measure the size of the air duct/drywall opening. Do not measure the overall size of the register itself, only measure the ""hole"" in the wall/duct. Every grille has a front end frame, that will overlap at wall joint. Width vs Height The first number in a grille size, represents the width, the second number represents the height. Example: If your hole is 20"" wide by 14"" tall, order a 20x14. If your hole is 14"" wide by 20"" tall, order a 14x20.