Door Size Calculator

When installing a door, the rough opening in your wall must be slightly larger than the door itself to allow for framing, shimming, and clearances. Enter your door width, door height, door thickness, frame type, clearances, shim space, and sill type into the Door Size Calculator to get the exact rough opening width your wall needs. Secondary outputs include rough opening height, frame width required, and frame height required.

in

Standard door width (24", 28", 30", 32", 36")

in

Standard door height (78", 80", 84", 96")

in

Gap between door top and frame

in

Gap between door sides and frame

in

Gap between door bottom and floor/threshold

in

Space for shimming and adjustment

Results

Rough Opening Width

--

Rough Opening Height

--

Frame Width Required

--

Frame Height Required

--

More Construction Tools

Frequently Asked Questions

What is a rough opening and why is it important?

A rough opening is the framed opening in a wall where a door will be installed. It must be larger than the actual door to accommodate the frame, shims, and proper clearances for installation and operation.

How much clearance should I leave around my door?

Standard clearances are typically ⅛" on top and sides, and ¼" on the bottom. These gaps allow for proper door operation, seasonal wood movement, and carpet or flooring thickness.

What's the difference between interior and exterior door thickness?

Interior doors are typically 1⅜" thick, while exterior doors are usually 1¾" thick for better insulation and security. Heavy-duty applications may use 2" thick doors.

How much shim space do I need for door installation?

Allow at least ½" of shim space around the door frame for proper leveling and square adjustment. This space is crucial for achieving a professional installation.

Do I need different calculations for different frame materials?

Yes, different frame materials have varying thicknesses and installation requirements. Steel and aluminum frames may require different clearances compared to wood frames.

What if my door opening is not standard size?

Custom doors can be made to fit non-standard openings. However, it's often more cost-effective to modify the opening to fit standard door sizes when possible.

Should I include the threshold in my height calculations?

Yes, if installing a raised threshold or adjustable sill, add its height to your rough opening calculations. Standard thresholds are typically ¾" to 1¼" high.

How do I measure an existing door opening?

Measure the width at three points (top, middle, bottom) and use the smallest measurement. For height, measure both sides and use the shortest. Always measure to the nearest 1/16".