Header Size Calculator

1. Enter the opening width in feet.
2. Pick the building width (12, 24 or 36 ft).
3. Pick the load above (roof only or floor plus roof).
4. Pick the wall type (bearing or non-bearing).
5. Read the recommended header, span, jack studs and king studs.

Here is what each result line means:

For the stud count and plate stock for the whole wall, see the stud calculator or the framing calculator.

A header size calculator tells you which doubled lumber beam fits a door or window opening in a load-bearing wall. It uses the IRC R602.7 span tables so you can pick the right header without looking up the code yourself.

Framers, builders and permit applicants use it to size headers before submitting plans or buying lumber.

The calculator looks up the IRC R602.7 exterior bearing wall table for your building width and load condition. It finds the smallest doubled header whose tabulated span is at least as wide as your opening.

1. Convert the opening width to inches.
2. Look up each header size (2-2×6, 2-2×8, 2-2×10, 2-2×12) in the table for the chosen building width and load.
3. Pick the first header whose span meets or exceeds the opening.
4. Read the jack stud count from the same table row.
5. Assign king studs: 1 per side up to 8 ft, 2 per side over 8 ft.

You have a 5-ft door opening in a bearing wall of a 24-ft-wide building supporting only the roof and ceiling.

Lookup: 2-2×6 spans 4 ft 7 in (too short). 2-2×8 spans 5 ft 9 in (fits). Jack studs = 1 per side. King studs = 1 per side (opening under 8 ft). Use a doubled 2x8 header.

Building Width

A wider building puts more tributary load on the header. A header that spans 6 ft in a 12-ft building may only span 4 ft in a 36-ft building.

Load Condition

A wall supporting one floor plus a roof carries roughly twice the load of a wall supporting only a roof. Headers shrink accordingly.

Bracing

IRC R602.7 assumes the header top is braced by perpendicular framing. Without bracing, spans for 2×8, 2×10 and 2×12 headers must be multiplied by 0.70.

Species and Grade

The IRC tables assume minimum #2 grade of any listed species group. Higher grades or stronger species allow longer spans under engineered design.

Snow Load

The standard table uses 30 psf ground snow load. Heavy-snow regions may reduce allowable spans.

The table below shows doubled header spans for an exterior bearing wall supporting roof and ceiling only (IRC R602.7(1), 30 psf snow, #2 grade).

Values are from IRC Table R602.7(1). Wider buildings reduce the allowable span.

New Construction Permits

Size every header before submitting plans for review.

Window and Door Replacements

Verify the existing header is adequate if you widen an opening.

Garage Door Headers

Wide garage openings often exceed standard tables and need engineered beams, but the calculator shows exactly where the cutoff falls.

Non-bearing Partitions

Confirm that a flat 2×4 is enough and skip the doubled header entirely.

1. Using the Wrong Building Width

The building width is measured perpendicular to the header, not along the wall. A wrong width gives the wrong table column.

2. Ignoring the Bracing Factor

If cripple studs sit on top of the header with no perpendicular bracing, spans for 2×8 through 2×12 must be reduced by 30 percent.

3. Forgetting Jack Studs

The header rests on the jack studs. Using fewer than the table requires can cause the header to deflect or fail inspection.

4. Treating Non-bearing Walls Like Bearing Walls

A doubled header in a non-bearing wall wastes lumber. A flat 2×4 handles openings up to 8 feet.

5. Exceeding the Table

Openings wider than the largest tabulated span need an engineered header (LVL or steel). The standard table does not cover them.

The calculator uses IRC R602.7(1) spans for exterior bearing walls with #2 grade lumber, 30 psf ground snow load. Interior bearing walls (Table R602.7(2)) have slightly different values not included here.

At 24-foot building width with roof load only, a doubled 2×6 spans 4 ft 7 in, which covers a 3-foot opening with margin.

At 24-foot building width under roof load, a doubled 2×10 spans 6 ft 10 in. Under floor-plus-roof load, a doubled 2×12 spans 6 ft 8 in.

No. IRC R602.7.4 allows a flat 2×4 across openings up to 8 feet in non-bearing walls. No jack studs or cripples are required.

If the top of the header is not braced by perpendicular framing, the IRC reduces allowable spans for 2×8, 2×10 and 2×12 headers by 30 percent. The 2×6 is exempt.

The IRC table specifies 1 or 2 per side depending on the header size and span. Generally, 2-2×6 and 2-2×8 need 1, while 2-2×10 and 2-2×12 need 2.

One king stud per side for openings up to 8 feet. Two per side for openings over 8 feet.

The IRC R602.7 tables apply to any #2 grade species group (SPF, Hem-Fir, Douglas Fir-Larch, Southern Pine). Higher grades or engineered lumber can span farther.

Yes. Laminated veneer lumber (LVL) headers span farther than dimensional lumber. Size them using the LVL manufacturer tables, not the IRC standard tables.

A 16-foot garage opening exceeds all standard doubled-lumber spans. Use an engineered beam (LVL, glulam or steel) and have it designed by an engineer.

No. The calculation runs entirely in your browser and nothing you enter is stored or sent anywhere.

• International Code Council, IRC R602.7 Table R602.7(1) (header and girder spans for exterior bearing walls).
• up.codes, IRC 2021 Chapter 6 Wall Construction (IRC R602.7 text and footnotes).
• City of Waterloo IA, Header Sizing Handout (IRC R602.7 summary with king stud rules).
• Fine Homebuilding, The Right Header for Every Wall (non-bearing header rules and framing practice).