Door Header Size Calculator
Learn how to size a door header: enter your rough opening width and wall type to get the right header lumber size — single or double 2x4 through 2x12 — plus jack stud count, overall header length, and board feet. Includes a door header span table and a door header size chart for common openings, in inches or millimeters.
Size your door header
Measure the rough opening (stud to stud), not the door slab. A 36-inch door usually needs a 38-inch rough opening — but enter whatever your framing measures.
Rule of thumb only — verify with your local building code and a structural engineer before you build.
Door header size chart
Rule-of-thumb spans for common rough openings, generated from the same tables as the calculator. The double 2x12 header max span in this table is 72 inches (6 feet) for a single-story load bearing wall — wider needs engineered lumber. For example, the door header size for 32 inch door openings is a double 2x6 in a bearing wall and a single 2x4 in a non bearing wall.
Common door openings
Quick reference for standard door sizes (rough opening = door slab + about 2 inches).
| Opening | Load-bearing (1 story) | Non-load-bearing |
|---|
Load-bearing vs non-load-bearing walls
A load-bearing wall carries weight from above — floor joists, roof rafters, or another wall — down to the foundation. Its header must be a real structural beam (doubled 2x lumber). A non-load-bearing wall only holds up itself and the drywall, so its header is just a nailing surface (single 2x).
How to tell which you have:
- In the attic or basement, check the joist direction. A wall running perpendicular to the joists is usually bearing them — load-bearing. A wall running parallel to the joists usually is not.
- Walls stacked directly over walls or beams below, and most exterior walls, are typically load-bearing.
- If a wall was added during a remodel and does not line up with framing above or below, it is often non-load-bearing.
When in doubt, treat it as load-bearing and have a structural engineer confirm before you cut — an undersized header sags, cracks drywall, and can bind the door.
How to size a door header — the rule of thumb
Framers have long used a simple rule of thumb: in a load-bearing wall, allow roughly 1 inch of header depth per foot of span, built as doubled 2x lumber. That gives double 2x6 up to 3 feet, double 2x8 up to 4 feet, double 2x10 up to 5 feet, and double 2x12 up to 6 feet for a single story. This calculator follows that conservative version of the rule.
The rule is intentionally conservative: the actual IRC span tables (R602.7) vary with lumber species, grade, building width, and snow load, and sometimes allow a bit more. That is exactly why this page keeps repeating itself: rule of thumb only — verify with your local building code and a structural engineer before you build.
Metric and Australia
Searching for door header size australia? The spans are the same physics everywhere — only the units change. A 900 mm rough opening (about 36 inches) in a load bearing wall still wants the equivalent of a double 2x6: two 90 × 45 mm members. Switch the calculator to centimeters and every answer converts automatically.
Frequently asked questions
What size header for a 36 inch door?
For a standard 36 inch door in a load bearing wall, this door header size calculator recommends a double 2x6 header. Cut it 39 inches long overall: 36 inches for the rough opening plus 1.5 inches of bearing on the jack stud at each end. That is about 2.23 board feet per ply, or 4.47 board feet total for both plies. In a non load bearing wall the same 36 inch opening needs only a single 2x4 nailing header, also 39 inches long.
What is the maximum double 2x10 header span for a door?
Under the rule-of-thumb table used here, a double 2x10 header spans up to 60 inches (5 feet) in a single-story load bearing wall. So the door header size for 60 inch opening in a bearing wall is a double 2x10, cut 63 inches long overall, which works out to about 6.07 board feet per ply (12.14 board feet total). If the wall carries a second floor as well as the roof, limit a double 2x10 to 48 inches and step up to a double 2x12 for wider openings.
What size header for a non load bearing door opening?
A non load bearing door header size does not need to carry structural load, so it is just a nailing surface for the framing above: a single 2x4 laid flat works for openings up to 48 inches, and a single 2x6 for openings up to 72 inches. For example, a 36 inch opening in a non bearing wall needs only a single 2x4, 39 inches long (about 1.42 board feet), with short cripple studs above it to back the drywall. Never use a single 2x4 in a load bearing wall.
How many jack studs for a door header?
Use one jack stud under each end of the header for openings up to 72 inches (6 feet), and two under each end for wider openings. Building code requires at least 1.5 inches of bearing at each end, so add 3 inches to the rough opening for the header length with one jack per side: a 36 inch opening takes a 39 inch header. Jack studs sit inside full-height king studs, which carry the load down to the floor.
How do I know if my wall is a load bearing wall?
Check the framing above and below. In the attic or basement, look at which way the joists run: a wall that runs perpendicular to the joists is usually carrying them, so it is load bearing; a wall parallel to the joists usually is not. Walls stacked over walls or beams below, and exterior walls, are typically load bearing. Getting the load bearing wall door header size right matters because an undersized header can sag or crack finishes. When in doubt, have a structural engineer confirm before you cut.
What is a door header in framing?
A door header is the horizontal beam that bridges the top of a door opening and carries the weight of the wall, floor, or roof above it down into the jack studs on each side. A typical wood header is built from doubled 2x lumber with a plywood spacer so it sits flush in the wall, supported by jack studs nailed inside full-height king studs, with short cripple studs filling the space above. For a longer beam run rather than a single door opening, a dedicated beam load calculator covers reactions, shear, and deflection — see the related tool link below.
What is the difference between a door header vs lintel?
They do the same job but the words come from different trades. Header is the wood-framing term for the built-up lumber beam over a door or window opening. Lintel is the masonry and steel term for the beam over an opening in a brick, block, or concrete wall, often a steel angle, a precast concrete unit, or a reinforced bond beam. This calculator sizes wood door headers; a brick or block opening needs a lintel sized to masonry rules instead.
When do I need an LVL header for a door opening?
You need an LVL header for door opening widths beyond this rule-of-thumb range: over 72 inches in a single-story load bearing wall, or over 60 inches when the wall also carries a floor. LVL and PSL engineered lumber are stronger and stiffer than sawn 2x lumber, so they can span farther, but they must be sized from the manufacturer's span tables for your load and span, not from a rule of thumb. Get a structural engineer to confirm the size, and verify with your local building code before you build.
Sources and method
- Header sizing follows a conservative rule-of-thumb simplification of the wood header span concept in IRC Section R602.7 (girders and headers). Real code tables vary by species, grade, building width, and ground snow load — always check the adopted code in your jurisdiction.
- Jack stud count and the 1.5-inch minimum bearing follow the convention of IRC R602.7.1.
- Actual lumber dimensions: 2x4 = 1.5 × 3.5 in, 2x6 = 1.5 × 5.5 in, 2x8 = 1.5 × 7.25 in, 2x10 = 1.5 × 9.25 in, 2x12 = 1.5 × 11.25 in (nominal vs. actual).
- Board feet = (thickness × width × length in feet) ÷ 12, per standard lumber measure.
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