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Calculation Machine

Door Rough Opening Calculator

Rough opening size and header length for any door.

Reviewed by James Whitfield · How we check our maths

Your values

ⓘ Live results

Results
Rough opening width
34.5 in
Rough opening height
82 in
Header length
37.5 in (RO + two jack studs)
King stud spacing
40.5 in
Finished opening
32 x 80 in

Working

  1. 132 + 2 x (0.75 + 0.5) = 34.5 in wide

Quick answer

Rough opening = door width + 2 inches and door height + 2.5 inches for a pre-hung door, giving room for jambs and shims.

The formula

RO width = door width + 2 in; RO height = door height + 2.5 in

Worked example

Worked example

Using the values the calculator loads with.

Inputs

  • Door width32 in
  • Door height80 in
  • Shim allowance each side0.5 in
  • Jamb thickness0.75 in
  • Floor clearance0.75 in

Result

  • Rough opening width34.5 in
  • Rough opening height82 in
  • Header length37.5 in (RO + two jack studs)
  • King stud spacing40.5 in
  • Finished opening32 x 80 in

How to use the Door Rough Opening Calculator

  1. 1Measure the door slab, not the old opening.
  2. 2Keep the default 1/2 inch shim space each side unless your framing is unusually true.
  3. 3Size the header for the span and load above the opening.

Frequently asked questions

What is the rough opening for a 32 inch door?

About 34 inches wide by 82.5 inches high for a standard pre-hung interior door.

Can the opening be too big?

Slightly oversized is fixable with extra shims, but more than an inch of slop makes the jamb hard to hold plumb and square.

About this calculator