Start by measuring the width of the prehung door from the interior. Measure from one side to the other of the door panel, or the part that swings. To find the door height, measure from the top of the door panel to the bottom on the edge of the door. Measure the door thickness and door jamb width.
Start by measuring the width and height of the existing door slab. Round each number up to the nearest inch to determine the nominal door size you'll need. For single doors and doors with sidelites, measure only the door slab. For Double Doors, measure the width of the two door slabs together.
For reference, standard interior door widths range from 24"-36" (finished opening). While a standard door height is 80" (finished opening). The difference between a rough opening and finished opening is usually 2-3 inches.
In the case of a standard 36" x 80" pre-hung single door, you will need a rough opening that measures approximately 38-1/2" x 82-1/4".
Take three measurements inside the door frame – at the top, middle and bottom. The widest measurement determines the width of the door. Use a tape measure to understand the width of the three areas of the door frame. Run the tape measure along the width of the frame from the left to the right and record these numbers.
To determine the total width you'll need for the opening, add the door's width (32 inches) to the frame's thickness of 1 3/8 inches. So, if you have a 32-inch door with a standard frame, your rough opening should be 33 3/8 inches wide.
For example, a nominal door size of 36 inches would fit into a rough opening 36 inches wide. The actual size of the door slab may be slightly smaller than the nominal size, typically by about 3/4 inch on each side, allowing for clearance around the door to ensure it can open and close smoothly.
A typical header width with single jack studs is cut 3″ larger than the rough opening. An example: A 36″ door has a rough opening width of 38″ so your header is cut at 41″. Also, be aware double or triple jack studs may be required based on the opening width and the load the header carries.
There should be a 2mm or 3mm gap between the door and the frame on both sides and the top. If you do need to cut the door down to size, keep in mind that you need to cut all four sides of the door equally whenever possible to retain an accurate shape or pattern if the door is panelled.
The width of the door you choose could directly affect aesthetics, but most often, door widths are selected for practical reasons. The most common interior door width found in a bedroom is 30 inches.
The minimum width of each door opening shall be sufficient for the occupant load thereof and shall provide a clear width of not less than 32 inches (813 mm). Clear openings of doorways with swinging doors shall be measured between the face of the door and the stop, with the door open 90 degrees (1.57 rad).
A pre-hung door is a door set consisting of everything that you need to install it into your opening. A slab door is simply just the door. A slab door is included in pre-hung doors. The difference being that the slab door in a pre-hung set will come with the frame and hinges already attached.
A rough opening is the space cut out of a wall where a window or a door will get mounted. Technically, the rough opening is the structural frame that surrounds the door unit. The dimensions for the rough opening are from jack stud to jack stud (vertical studs) and from header to floor.
Headers come in all sizes, and usually a structural engineer or an architect will size them for you. A doorway in a non-load-bearing wall doesn't need a structural header. You'll place just one or two 2x pieces of lumber flat across the top of the opening.
However, for a street car, Don recommends the following guidelines: 200-325 horsepower look for 1 1/2-inch primaries, 275-425 horsepower use 1 3/4-inches, 400-500 horsepower opt for 1 3/4 to 2 inches, and 500+ horsepower look for 2 inches or greater. Keep in mind, smaller pipes mean more low-to-mid-range torque.
Standard door heights are 6/6 (78”) and 6/8 (80”). In addition, special sizes can sometimes be custom ordered. A 36” x 80” pre-hung single door will use a rough opening of approximately 38-1/2” x 82-1/4” to fit. Always remember to square up your door before you nail the frame in place to assure it will close properly.
Add 10mm to the door height to get the reveal height. Add 48mm to the door height to get the overall height. Subtract 30mm from the reveal width to get the clear opening width. Subtract 15mm from the reveal height to get the clear opening height.
While homes come in all shapes and styles, most entry doors follow some common measurements. The most typical standard door width is 36 inches, paired with a height of 80 inches.
A rough opening is the space in your wall where the door will be installed, and it needs to be larger than the actual door itself to accommodate the door frame, shims, and any necessary adjustments. For a standard 36-inch exterior door, the rough opening should typically be 38 inches wide and 82.5 inches tall.
By ADA standards, the clear width of a door opening must be a minimum of 32 inches. This clear width measurement is taken between the face of the door and the stop of the frame with the door open to 90 degrees (Figure A). In pairs, at least one of the active leaves must comply with this clear width requirement.
Framing rough opening sizes are really quite simple. Just add 2″ to the width of the actual door size. You should add 2-1/2″ to the height of the actual door. This will give you room to space the door frame off of the sub-floor.