4" X 18" Is The Size For The Duct Opening Measurement Only, Actual Front End Outer Dimensions Are 5.75 Width X 19.75 Height - SEE BELOW IN DESCRIPTION HOW TO MEASURE A GRILLE HVAC 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! High Standard Every part is hand inspected for quality before it is packaged, no exceptions. No Sharp Surface Edges - Just run your finger along the edge of the top plate and you will find a smooth finished surface. Quality Packaging - Carefully Shrink Wrapped With Cardboard Backing To Prevent Damage In Shipment Easy Unrestricted Air Flow For Your HVAC System 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. Total outer size of this grille is; listed size + 1.75" at width and + 1.75" at height. 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." 100% Satisfaction Guaranteed Don’t worry, you’re covered by our 100% money back guarantee no questions asked. Click Add to Cart Now! and enjoy a new updated refreshing look to your home.