Complete Door Frame Height Chart & Buying Guide: Standard Sizes, Casing Types, and Custom Fits
Blueprint schedules display nominal dimensions that do not match the real-world measurements carpenters cut into framing packages. When an architectural plan lists an interior passage as a "2/8 x 6/8" door, it specifies a door slab measuring 32 inches wide by 80 inches tall. It tells you nothing about the total clearance needed for the frame, the threshold, or the level adjustments.
The actual outside dimensions of a pre-hung door frame exceed the slab size. A typical 80-inch door frame features a 3/4-inch-thick head jamb, plus an extra 1/8-inch gap between the top of the door slab and the jamb itself. Underneath, manufacturers leave between 1/2 inch and 3/4 inch of jamb leg extension to allow the door to swing cleanly over finished floor coverings. Consequently, a pre-hung assembly for an 80-inch slab measures roughly 81-5/8 inches to 81-3/4 inches in actual outside height.
Rough openings must be larger still. Framing rough opening dimensions must accommodate the jamb thickness, factory clearances, and an intentional shim space allowance of roughly 1/2 inch at the top and 1/4 to 1/2 inch along each side. Without this margin, out-of-plumb king studs or out-of-level subfloors make hanging a plumb, square jamb impossible without cutting into structural framing.
