Garage Door Rough Opening Calculator

Header Selection by Opening Width & Bearing Load

A simplified selection guide cross-referenced to IRC R602.7. Openings over 16′, or any opening carrying a second-floor or roof load, require an engineered LVL header stamped by a licensed structural engineer — dimensional 2×12 lumber does not span a 16′ opening under bearing load without excessive deflection. For the full dimensional-lumber span table and 2×12 header depth, see the 2×12 Lumber Calculator.

Single-story bearing = roof + ceiling only. Two-story bearing = roof + one floor + attic. LVL headers must be sized via manufacturer published tables (e.g., NER-272) and stamped for permit.

Framing an Exterior Garage Door Wall (Whole Wall + Rough Opening Integrated SOP)

This page focuses on the rough opening math for the door itself — but when you actually frame exterior wall segments like the whole garage-front facade, the opening is only one slice of a 9-step assembly that also has to hold up the trusses, shed water, and accept the OSB sheathing break on stud centers. The SOP below ties the garage-door RO calculator output back into the full wall-framing sequence, so you never run into the classic "the opening is perfect but the sheathing won't cover it" problem. For the general frame exterior wall knowledge base covering interior and exterior bearing walls, including the annotated SVG diagrams of king/jack/header/cripple assemblies, see the Wall Framing Diagram guide.

1. 1

   Slab anchor layout & sill-sealer bed

   Snap two chalk lines on the slab: one for the back edge of the PT sole plate, one for the front edge. The gap between them is exactly 3-1/2″ (2×6 exterior = 5-1/2″). Lay a 1/8″ closed-cell foam sill sealer or a 10-mil poly strip under the full plate length — do not skip this; it is the #1 air-leak point on a garage front. Shoot 5/8″×3-1/4″ concrete nails or powder-actuated pins every 24″ O.C., with one pin within 12″ of each plate end.

2. 2

   PT bottom plate + mark O.C. 16″ sequence AND the RO markers

   Lay the full-length PT plate on the sill sealer. On the same plate, pencil both the general 16″ O.C. marks for the infill studs (15-1/4″ first, then 31-1/4″, 47-1/4″…) AND the two king-stud marks for the garage-door RO. The king-stud marks override any O.C. marks they fall on — the infill stud spacing re-starts after each king. Run the same double-marked sequence on the (2 plates of the) double top plate.

3. 3

   King studs: plumb, brace, snap-to-line install

   Toenail two 16d galvanized nails through each king-stud toe into the PT sole plate, then plumb with a 6′ level, attach temp 2×4 diagonal braces, and toenail the top into the double top plate. Verify the face-to-face distance between the two kings equals the RO width from the calculator (e.g. 9′-2″ for a 9′ door). This is the critical dimension — everything else (jacks, header, cripples) nests inside it.

4. 4

   Jack (trimmer) studs under header ends + header cut/seat

   Cut jacks to height = RO height minus header depth. For a 2-ply 2×12 header the jacks sit flush against each king, face-nailed with three 16d at 16″ O.C. Set the header onto the jacks from inside — the header ends should extend 1-1/2″ past the jack center (bearing). For an LVL engineered header, use 1/2″ galvanized through-bolts to tie the LVL plies together at 24″ O.C. staggered before setting, not after.

5. 5

   Cripple studs above header to double top plate

   Cripples = (wall_top_plate_bottom_y − header_top_y) cut length. Spacing = 16″ O.C. snapped from the nearest corner — do not use 24″ spacing above a garage door header; the OSB above the door is 2 ft tall, and 24″ cripples leave the 4-ft sheet edge unsupported. Face-nail each cripple with two 16d into the double top plate and two 16d into the header top.

6. 6

   Infill studs (exterior-wall segments left & right of the door)

   Drop in the remaining studs following the 15-1/4″ first-stud rule from the nearest outside corner. For 2×6 exterior walls the stud cut length is 92-5/8″ (standard precut). Face-nail top and bottom with two 16d each end. Sheathing edge check: every 48″ mark should fall dead on a stud center — if any mark is off more than 1/8″, snap and re-mark the plate rather than force the sheet.

7. 7

   Door-unit clearance check before sheathing

   Slab + PT plate bottom to header-bottom should read the exact RO height from the calculator (e.g. 7′-2-1/2″ for a 7′ door with 2.5″ allowance). Side jamb clearance: each side between king and door-leaf outer rail = ~1″ for jamb + track. Headroom above header: confirm 12″ minimum to any ceiling joist or opener rail — if you are under, you must use a low-headroom track, and now (before sheathing) is the cheapest moment to raise the header.

8. 8

   Fastening schedule + hold-downs for shear wall compliance

   Nail schedule on exterior wall studs: 16d common or 0.131″×3-1/4″ galvanized framing nails, two nails top + bottom for each stud into plates, 12″ O.C. on the plate edges, 6″ O.C. within 12″ of any corner or opening. Hold-down: if the local code requires a garage-front shear wall, add a metal hold-down strap from the king stud down into the slab — do not rely only on toenails through the PT plate; wind/seismic forces concentrate on the door corners.

9. 9

   Sheathing + cap flashing over the header (the most-omitted step)

   Hang 7/16″ OSB vertically with H-clips or 3/8″ stagger on edges. Nail at 6″ O.C. on sheet edges and 12″ O.C. in the field. Install a Z-cap or peel-and-stick flashing over the header top edge, lapping up behind the house-wrap / rigid-foam seam by at least 6″. This flashing, not the header wood, is what prevents the #1 call-back: water getting behind the door track and rotting the header end-grain through the jack-stud top.

Garage Door Rough Opening FAQ