HOW THE SIZING WORKS...

All of our products and sizes are ordered and built based on the FINISHED dimensions (that is, AFTER the product is installed, it's the clear space you'll have available).  Because you're installing something into your current opening, the ROUGH opening must be a little bigger.  Here's a quick sketch to illustrate how the arch unit fits WITHIN the rough framed opening:

FOR EXAMPLE: If you have a current framed opening of 50" in width, the correct arch kit to order would be the 48" FINISHED size.

The same goes for the height: A FINISHED height arch of 92" would require a ROUGH framed height of 94".

CALL OR EMAIL FOR MORE INFORMATION.  WE'RE ALWAYS HAPPY TO ANSWER QUESTIONS.