Measuring Door Size

Before selecting a new door, it’s essential to measure the rough opening – the framed space where the door and jamb will be installed. A precise measurement ensures a perfect fit, smooth operations, and a polished final look.

How to Measure Width

  1. Measure the rough opening width from the stud in three places – top, middle, and bottom
  2. Use the smallest measurement to ensure accuracy
  3. Subtract 2 inches from this number to determine the correct door width

Example: A rough opening width of 38 inches means you need a 36-inch (3/0) door. 

How to Measure HEIGHT

  1. Measure from the floor to the underside of the upper stud at both corners of the opening
  2. Use the smaller measurements for precision
  3. Subtract 3 inches from this number to get the correct door height

Example: A rough opening height of 99 inches means you need a 96-inch (8/0) door.

Note: These measurements are using the standard jamb thickness of 3/4″. If opting for a thicker jamb application, door size will need to be adjusted accordingly.

Framing a New Rough Opening?

If you’re building a new wall frame, reverse these calculations: add 2 inches to your desired door widths and add 3 inches to your door height.

Why the Extra Space?

Rough openings are intentionally larger than the door itself to allow for: 

  • Precision adjustments: Stud walls aren’t always perfectly plumb and square, so extra space lets you fine-tune alignment with shims.  
  • Flooring clearance: Interior doors need room for carpets, wood, or tile; exterior doors require space for the sill. 
  • Seasonal shifts: Wood structures naturally expand and contract with humidity changes, so this buffer ensures long-term functionality. 

By following these steps, you’ll see the foundation for a smooth, professional-quality door installation.