Door Rough Opening Dimensions & Sizing
Direct Answer
Door rough openings are standardized framing openings in wood and steel stud walls engineered to accept pre-hung door frames, shims, and finished jambs. Under standard architectural guidelines, rough opening width is calculated as Nominal Door Width + 2.0 inches, and rough opening height is calculated as Nominal Door Height + 2.5 inches, with standard 36×80" doors accommodating ADA accessibility.
Source: WDMA I.S. 1-A / ADA Standards for Accessible Design 2010
Specs
| Governing Standards | WDMA I.S. 1-A / ANSI A250.8 / ADA Standards Section 404 |
| Rough Opening Width Formula | Nominal Door Width + 2.0 inches (51 mm) |
| Rough Opening Height Formula | Nominal Door Height + 2.5 inches (64 mm) |
| 30×80" Bedroom Door (2/6 × 6/8) | Rough Opening: 32.0 × 82.5 inches (813 × 2096 mm) |
| 32×80" Standard Entry (2/8 × 6/8) | Rough Opening: 34.0 × 82.5 inches (864 × 2096 mm) |
| 36×80" ADA Entry (3/0 × 6/8) | Rough Opening: 38.0 × 82.5 inches (965 × 2096 mm) |
| Standard 2×4 Wall Jamb Depth | 4-9/16 inches (116 mm) = 3.5" stud + two 1/2" drywall layers |
| Standard 2×6 Wall Jamb Depth | 6-9/16 inches (167 mm) = 5.5" stud + two 1/2" drywall layers |
The Universal Rough Opening Sizing Rule
When framing door openings with wood king and jack studs, carpenters utilize the universal rule of thumb: $$\text{Rough Opening Width} = \text{Door Width} + 2.0\text{ inches}$$ $$\text{Rough Opening Height} = \text{Door Height} + 2.5\text{ inches}$$
This extra allowance provides:
- $1.50\text{ inches}$ for the two $3/4\text{-inch}$ solid wood side jambs.
- $0.50\text{ inches}$ of total side-to-side shim space ($1/4\text{ in}$ per side) to plumb the jamb in imperfectly vertical stud walls.
- $2.50\text{ inches}$ in height to accommodate the $3/4\text{-inch}$ top head jamb, $1/2\text{-inch}$ top shim gap, and $1\text{-}1/4\text{-inch}$ floor clearance for carpet/hardwood.
ADA Accessibility Requirements (36-Inch Doors)
Section 404 of the ADA Standards for Accessible Design mandates a minimum clear opening width of $32.0\text{ inches}$ ($813\text{ mm}$) measured between the face of the door (open at $90^\circ$) and the opposing door stop. Because the door slab thickness ($1\text{-}3/4\text{ in}$) and hinge projection intrude into the opening, a $36\text{-inch (3/0)}$ door (rough opening $38\times 82.5\text{ in}$) is required to achieve full ADA legal compliance.