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Door rough opening

A door rough opening is the prehung unit's frame size plus the maker's allowance; JELD-WEN asks for 1 in more width and 3/4 in more height. A unit 37-1/2″ × 81-1/2″ needs a 38-1/2″ × 82-1/4″ opening and a 41-1/2″ header.

Framing Calculators editorial teamUpdated 2 sources

Calculator

Door rough opening calculator

Unit size + allowance → rough opening, header, jacks and cripples.

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Type lengths the way you read a tape: 8' 9", 7 3/4 or 7.75. Metric: 2667 mm or 2.667 m.

RO 38-1/2″82-1/4″
Rough opening38-1/2″ × 82-1/4″width × height
Header41-1/2″two plies
Jack studs80-3/4″

Framing

King studs
92-5/8″full length, one each side
Cripples above the header
2-5/8″too short for cripples: use a flat 2x or a deeper header
Top of the rough opening
82-1/4″above the subfloor

Check the door maker's sheet: allowances differ by product line and some codes call for less.

How it works. Rough opening = unit (frame) size + allowance. Header = opening width + one 1-1/2 in jack each side. Jack = opening height − bottom plate. Cripples above = (plate + stud length) − (opening height + header depth).

How to size a door rough opening

Size the rough opening from the door unit you will install, not from the slab: measure (or read) the outside of the frame on the prehung unit and add the allowance from its installation sheet. JELD-WEN's exterior prehung instructions want the unit 1 in narrower and 3/4 in shorter than the rough opening, or 1/2 in each where the code requires less[1]. Other makers use their own figures, so check the sheet for your door.

Framing around the opening

  • Header: rough opening width + 3 in, sized from IRC Tables R602.7(1) and (2) for bearing walls[2].
  • Jack (trimmer) studs: carry the header; the number per end comes from the header table[2].
  • King studs: full height beside the jacks; IRC Table R602.7.5 sets the minimum in exterior walls[2].
  • Nonbearing walls: need no structural header; a flat 2x4 can span openings up to 8 ft[2].

Common door opening mistakes

  • Sizing from the slab. The frame adds jamb thickness and clearances; use the unit size.
  • Forgetting the finish floor. Set the opening height from the finished floor the door will swing over.
  • Header that will not fit. A 2x12 header on an 8 ft wall can leave too little room for cripples; the calculator flags it. Window openings are on the window rough opening page, the whole wall on the framing calculator and the stud layout on the stud calculator.

Frequently asked questions

What is the rough opening for a door?

The door unit (frame) size plus the allowance in its instructions; for a JELD-WEN prehung exterior door, 1 in wider and 3/4 in taller than the unit.

How long is the header for a door?

The rough opening width plus 3 in, for one 1-1/2 in jack stud at each end.

How long are jack studs for a door?

The rough opening height less the bottom plate thickness, so the header sits at the top of the opening.

Does a rough opening calculator work for interior doors?

Yes. Enter the prehung unit size and the allowance from its sheet; interior walls that do not bear load need no structural header.

Sources

  1. Installation Instructions for Prehung Exterior Entry Doors (JII106) · JELD-WEN, 2018, rev. 05/22
  2. 2021 International Residential Code, Chapter 6: Wall Construction (R602 studs, plates, headers) · International Code Council, accessed November 13, 2026