Door and window casing is the frame that completes the opening in a wall. A well-chosen casing makes a simple door look expensive; a mismatched casing makes an expensive door look cheap.
Casing Width
The casing width should relate to the wall thickness and the opening size. On a standard 2x4 framed wall with 1/2-inch drywall, a 2-1/4 inch casing is typically appropriate. On thicker walls or larger openings, wider casing is needed for proportional coverage.
Backband vs. Straight
A backband casing — where a secondary profile wraps the outer edge — adds depth and formality. Straight casing is cleaner and more modern. Match the casing style to the overall trim complexity in the room.