How to Calculate the Rough Opening of a Door
The rough opening is the hole cut into a wall, during construction, where your new door will hang. Most doors are pre-hung, which means the door is already attached to a frame; you install the frame around the rough opening. You need a hole that is slightly larger than the door and frame. The extra space allows you to slide the door into place easily and adjust it within the hole to ensure the frame is square. Installing the frame square is essential for the door to open and close without sticking.
Read the information provided by the door manufacturer. Look for specifications for the rough door opening if the information is provided. This gives you a general reference point to ensure the opening's measurements are suited to the door and frame you want to install.
Measure the width of the entire door and frame that is attached. Take accurate measurements to ensure the rough opening isn't too large or too small. Add 1 inch to the width of the door to calculate the width of the rough opening. The extra width allows the door to fit easily into the opening.
Measure the height of the entire door and attached frame. Add 1 inch to this measurement for extra space above and below the door for an easier fit.
Mark the measurements for the rough opening on the wall. Hold the door and its frame up to the wall to get a visual to ensure the door frame will fit within the opening you measured.
Things You Will Need
- Tape measure
- A minimum of 1 extra inch of width and height is necessary to install a door. You can add up to 2 inches total to the width and height if you want more working room, but avoid a space of more than 2 inches, as it is more difficult to fill in around the door when it is installed.
- While the rough opening is sized to hold the door and frame, you may need to cut a larger hole in the wall to account for vertical studs to hold the frame. The king studs and trimmer pieces run vertically along either side of the door frame. If using the standard 2-inch-by-4-inch boards, the two boards add about 3 inches on either side of the frame, for a total of 6 inches extra to the width.
- If the door you're adding is completely new on an existing home, you'll also need to account for a header board when calculating the height of the hole that you cut. This is particularly true on a load-bearing wall. Review building code to determine the requirements for headers. This helps you determine how large you need to cut the entire opening in the wall.