How do I calculate the rough opening for a door?

Add 2 inches to the door width (for two 3/4" jambs plus 1/4" shim space per side) and 2.5 inches to the door height (for sill plate, shim space, and header clearance). For example, a 32" × 80" door needs a 34" × 82.5" rough opening.

What is the minimum door width for ADA compliance?

ADA requires a minimum 32" clear opening width, which typically means installing a 34" door. The clear opening is measured from the face of the door to the stop when the door is open 90°. For new construction, 36" clear width is recommended.

What size header do I need for a 36-inch door?

For a 36" door (38" rough opening) in a load-bearing wall, use a doubled 2×8 header. For non-load-bearing walls, a doubled 2×4 cripple header is sufficient. Always check local building codes and consult an engineer for structural openings.

How tall should a standard door be?

Standard residential door height is 80" (6'8"). Taller options include 84" (7'), 96" (8'), and custom heights. ADA requires a minimum 80" clear height. Exterior doors and garage doors often use taller heights for headroom.

Door Sizing Calculator

Calculate rough opening dimensions, header size, ADA clearances, and framing materials for any door type and size

Door Specifications

Door Type

Width Presets (inches)

Door Width (in)

Door Height (in)

Height Presets (inches)

Wall Type

Header Clear Span (ft) Distance between king studs (typically door width ÷ 12 + 0.5)

Wall Thickness

Ceiling Height (in)

Rough Opening 34" × 82.5" W × H

RO Width 34"

RO Height 82.5"

Header Size 2×8 DBL

Jack Studs 2

King Studs 2

Cripple Studs 2

✓

ADA Compliant 32" clear width meets minimum requirement

Materials Summary

Shims (pairs) 9

Header lumber 2× 8-ft 2×8

Jack studs 2× studs

King studs 2× studs

Cripple studs 2× cripples

Rough Opening Width RO_W = Door Width + 2" 3/4" jamb × 2 + 1/4" shim each side

Rough Opening Height RO_H = Door Height + 2.5" Sill plate + shim space + header clearance

Cripple Studs (above header) n = floor(RO_W / 16) + 1 Based on 16" on-center framing

ADA Door Clearance Requirements

ADA Standards for Accessible Design (Section 404) govern door dimensions and clearances for commercial and public buildings. Many states have adopted similar requirements for residential accessibility.

Clear Opening Width

Hinge

DOOR

32"

Latch

Clear width measured from face of door to doorstop when door is open 90°

Minimum clear width 32" (door 34")

Recommended clear width 36" (door 38")

Double doors (active leaf) 32" min each

Maneuvering Clearance (Pull Side)

18" Latch side

32" Door width

12" Hinge side

60" depth min (pull side)

Pull side — latch clearance 18" min

Pull side — hinge clearance 12" min

Push side — latch clearance 12" min

Push side — depth 48" min

Pull side — depth 60" min

Hardware & Threshold

Handle Zone 34"–48"

Threshold ≤ 1/2"

↕ 48" AFF max

↕ 34" AFF min

↕ 80" clear height

Handle height min (AFF) 34"

Handle height max (AFF) 48"

Handle type Lever or loop (no knobs)

Threshold height max 1/2" (1/4" preferred)

Clear height minimum 80"

Opening Force

Interior doors 5 lbf maximum

Exterior doors No maximum (check local codes)

Fire doors Minimum per fire code

Closer Timing

Sweep period (open to latch) 5 seconds minimum

Measured from 70° open to 3" from latch

Sliding & Folding Doors

Sliding door clear width 32" min

Hardware Operable with closed fist

Pocket door clearance 18" latch side at pull

Standard Door Sizes & Rough Openings

All dimensions in inches. RO Width = Door Width + 2". RO Height = Door Height + 2.5".

Door Width	Door Height	RO Width	RO Height	Common Use	ADA Compliant
24"	80"	26"	82.5"	Closet, utility	No (20" clear)
28"	80"	30"	82.5"	Bedroom (tight)	No (24" clear)
30"	80"	32"	82.5"	Interior bedroom	No (26" clear)
32"	80"	34"	82.5"	Interior/accessible	Yes (28" clear*)
34"	80"	36"	82.5"	ADA standard	Yes (32" clear min)
36"	80"	38"	82.5"	Exterior/ADA preferred	Yes (34" clear)
24"	84"	26"	86.5"	Closet, taller ceilings	No
32"	84"	34"	86.5"	Interior 9-ft ceiling	Yes
36"	84"	38"	86.5"	Exterior 9-ft ceiling	Yes
32"	96"	34"	98.5"	Interior 10-ft ceiling	Yes
36"	96"	38"	98.5"	Exterior 10-ft ceiling	Yes
60" (French)	80"	62"	82.5"	French/double	Yes (each leaf 28"+)
72" (Garage)	84"	74"	86.5"	Single car garage	—
144" (Garage)	84"	146"	86.5"	Double car garage	—

* ADA clear width is measured from door face to stop at 90° open. A 32" door typically yields ~28.5" clear; 34" door yields ~32" clear.

Header Sizes by Span — Load-Bearing Walls (IRC R602.7)

For 2-story structures or roofs with rafter spans up to 26 ft. Double the lumber — two pieces with 1/2" plywood spacer to fill 2×6 wall depth.

Clear Span	Min Header Size (doubled)	Lumber Pieces	Notes
Up to 2 ft	2×4	2× 2×4	Light loads only
2–3.5 ft	2×6	2× 2×6	Single story or non-structural above
3.5–5 ft	2×8	2× 2×8	Standard single-story
5–7 ft	2×10	2× 2×10	Single story, heavy loads
7–9 ft	2×12	2× 2×12	Two-story or large openings
9–11 ft	4×12 or LVL	Engineered lumber	Consult structural engineer
Over 11 ft	LVL / PSL	Engineered lumber	Engineer required

Fire Door Ratings

Fire-rated doors are required between the garage and living space, in stairwells, and in commercial occupancies per IBC and IFC.

Rating	Min Door Construction	Common Applications	Self-Closer Required
20-minute	Solid-core wood or hollow steel	Corridor to stairwell, garage-to-house	Yes
45-minute	Solid steel or fire-rated wood	Stairwells in 1–2-hour assemblies	Yes
60-minute	Steel with intumescent seal	Openings in 2-hour fire walls	Yes
90-minute	Labeled steel, max 100 sq in glass	Openings in 3-hour fire walls	Yes

Always verify local amendments to IBC/IRC. Residential garage-to-house doors require 20-min rating or solid wood 1-3/8" min thickness (IRC R302.5.1).

How to Use This Calculator

Select door type — Interior, Exterior, Sliding, French/Double, or Garage. This affects ADA maneuvering clearance recommendations and typical framing approaches.

Enter door dimensions — Use the width and height presets for common sizes (32"×80" is the most common interior door), or type custom values.

Select wall type — Load-bearing walls require larger headers; non-load-bearing can use a simple 2×4 cripple header.

Read the rough opening — The calculator adds the industry-standard 2" to width and 2.5" to height for jambs and shim space.

Check ADA compliance — The status bar turns green if your door meets ADA minimum clear-width requirements (32" clearance at 90° open).

Key Terms

Rough Opening (RO): The framed opening in the wall, sized slightly larger than the door unit to allow for jambs and shimming.

Jack Stud (Trimmer): The vertical stud that sits directly under the header on each side and supports it. Cut to support the header height.

King Stud: Full-height stud that runs from bottom plate to top plate on each side of the rough opening, adjacent to the jack studs.

Cripple Stud: Short stud above the header that fills space between the header and top plate, typically spaced 16" on-center.

Header: Horizontal structural member that spans the top of the rough opening and transfers loads to the jack studs in load-bearing walls.

AFF (Above Finished Floor): Standard reference height for measuring accessible features like door hardware and switches.

Shim Space: The 1/4"–3/8" gap between the door frame and rough framing, filled with shims to plumb and level the door frame.

Clear Opening Width: The actual usable opening width measured from the face of the door to the stop, not the door leaf width.

Frequently Asked Questions

Why is the rough opening 2" wider than the door?

Each side of the door frame receives a 3/4" jamb (1.5" total) plus approximately 1/4" shim space per side (0.5" total) = 2" total added to the door width. Some framers add 2.5" for extra shimming room, especially on exterior doors.

What is the standard door size for a bedroom?

The most common bedroom door is 30"×80" or 32"×80". A 32" door is recommended because it meets ADA accessible design guidelines (provides approximately 28.5" clear opening). Modern construction often uses 36" doors for full ADA compliance.

Do I need a permit to replace a door in the same rough opening?

Like-for-like door replacements in the same rough opening typically don't require a permit in most jurisdictions. However, enlarging the opening, changing a window to a door, or adding a new opening almost always requires a permit. Check with your local building department.

How do I know if a wall is load-bearing?

Load-bearing walls typically run perpendicular to floor joists, sit over a beam or wall in the basement/crawlspace, or are centered in the building. Exterior walls are almost always load-bearing. Interior walls running parallel to the ridge line or over a center beam are usually load-bearing. When in doubt, consult a structural engineer before cutting.

What is a LVL header and when do I need one?

LVL (Laminated Veneer Lumber) headers are engineered beams with predictable, high strength. They are used for larger spans (typically 8+ feet) where standard doubled lumber would be insufficient, or where depth is limited. They don't warp or crown like solid lumber and are the preferred choice for large openings like garage doors or wide patio doors.

How many shims do I need to install a door?

A standard pre-hung door typically needs shims at the hinge locations (3 hinges = 3 spots, each needing 2 shims from opposite sides), at the strike plate, and at the top corners — approximately 8–12 pairs total. This calculator estimates about 3 pairs per foot of door height as a conservative material quantity.