What size header do I need for a 6 foot opening?

For roof and ceiling only, on a 28 ft wide building at 30 psf ground snow, two 2x10s span 7 ft 3 in and cover it with two jack studs each end. Change any of those three conditions and the answer changes; the table has 549 live cells for a reason.

How many jack studs does a header need?

From the same cell as the span, between one and four. Where the table calls for one, footnote d permits an approved framing anchor fixed to the full-height king stud instead of a jack stud altogether.

Does header span depend on the species of lumber?

Not in this table. Footnote b pools Douglas fir-larch, hem-fir, southern pine and spruce-pine-fir into one set of values assuming #2 grade, which means the numbers are governed by the weakest of the four. That is unlike the joist and rafter tables, which do split by species.

What is building width in the header table?

The width of the building measured perpendicular to the ridge, because that is what sets how much roof lands on the wall. The table gives 20, 28 and 36 ft, and footnote c permits interpolation between them.

What if my building is wider than 36 feet?

There is no prescriptive answer. Footnote c permits interpolation between the widths shown and nothing permits extrapolating past the last one, so the header has to be designed. This calculator stops rather than extending the trend.

Can I use this table for an interior wall?

No. Table R602.7(1) is for exterior bearing walls. Interior bearing walls are Table R602.7(2) and the spans differ, because an interior wall generally carries floor and ceiling but not roof and snow.

Does the table cover LVL or engineered beams?

No. It is dimension lumber at #2 grade. LVL, glulam and PSL are proprietary products sized from the manufacturer's own published span tables, and reading them off a code table for sawn lumber is meaningless.

Home › Structural › Header and Girder Size Calculator

Header and Girder Size Calculator

IRC Table R602.7(1), read cell by cell from the code

Sizing a header is a table lookup, and the table is bigger than people expect: five support conditions, fourteen sizes, three snow loads and three building widths, 549 live cells. Two of its footnotes change the answer and almost no calculator repeats them. One table serves four species, and where it calls for a single jack stud you are allowed to use none.

Header and girder span

The header supports

Header size

Ground snow load

Building width (perpendicular to the ridge)

Clear opening

Stud spacing

Wall type

Every figure is a cell in Table R602.7(1). Interpolation between building widths is permitted; extrapolation past 36 ft is not.

Specification summary

Generated from on . Reopen that address to reproduce these figures exactly.

Entered

Result

The opening in elevation: header, jacks and kings

Worked example

A 6 ft opening in an exterior bearing wall carrying roof and ceiling only, on a 28 ft wide house, 30 psf ground snow, two 2x10s.

The cell. Roof and ceiling, 2-2x10, 30 psf, 28 ft wide: 7 ft 3 in with 2 jack studs each end.
Your 6 ft opening fits, with 1 ft 3 in to spare.
Drop to a 2-2x6 and the cell gives 4 ft 8 in. The same opening now fails and no amount of nailing fixes it.
Go up to a 4-2x8 instead and the cell gives 8 ft 4 in with one jack stud, which means a framing anchor is permitted in its place.
Widen the house to 36 ft and the 2-2x10 drops to 6 ft 6 in. Building width matters as much as the member.

That last step is what people miss. The header does not know how wide your opening is until it knows how much roof is landing on it, and roof area scales with the width of the building, not the width of the hole.

The formula

No formula. A lookup, with one interpolation the code explicitly permits:

span = table[support][size][snow][width] RO = clear + 2 × 1.5 × NJ

support: which of the five load paths lands on this header
size: plies and depth, e.g. 2-2x10 is two 2x10s
snow: ground snow load, psf. Under 30 uses the 30 column
width: building width perpendicular to the ridge, ft. Interpolated between 20, 28 and 36
NJ: jack studs each end, from the same cell

Rough opening is the clear span plus the jack studs at each end, so the jack count is not just a strength question, it decides how big a hole you have to frame. Two jacks each end costs 3 in of rough opening against one.

The two footnotes that change the answer

Table R602.7(1) is reproduced all over the internet and its footnotes almost never are. Two of them matter more than most of the cells.

Footnote b. One table serves Douglas fir-larch, hem-fir, southern pine and spruce-pine-fir. That is unusual: the joist and rafter tables split by species because the species differ, and here they are pooled. Pooling means the table is built on the weakest of the four. Your southern pine header genuinely is stronger than this table says, and the prescriptive path gives you no way to claim it. To use the real number you leave the table and design the member.

Footnote d. Where the table calls for one jack stud, an approved framing anchor fixed to the full-height king stud may carry the header instead. That is a real permission, not a workaround, and it buys 1 1/2 in of rough opening at each end. On a window schedule that is occasionally the difference between the unit fitting and not.

The third thing to know is what the table does not do. Footnote c permits interpolation between the building widths shown. Nothing permits going past 36 ft, or past 70 psf ground snow, and this page refuses both rather than extending a line off the end of a chart.

Building width is doing more work than the opening

The instinct is that a header is sized by the hole. It is sized by the load, and the load is the roof and floor area that lands on that stretch of wall. The table encodes that as building width measured perpendicular to the ridge, because half the roof spans to each exterior wall.

So the same two 2x10s carry 8 ft 5 in on a 20 ft house, 7 ft 3 in on a 28 ft house and 6 ft 6 in on a 36 ft house, all at 30 psf. A quarter of the capacity disappears between the narrowest and widest case without the header changing at all.

Measure perpendicular to the ridge, not the long way along the house. It is a common and expensive misreading.

What this table is not

It is for exterior bearing walls. Interior bearing walls have their own table, R602.7(2), with different spans, because an interior wall carries floor and ceiling but usually not roof and snow. The calculator warns rather than silently serving you the wrong one.

It is dimension lumber only. LVL, glulam, PSL and steel are not in it. Those are manufacturer or engineered products sized from their own published tables, and substituting them into a code table is meaningless.

It says nothing about what holds the header up below. The jack studs land on a plate and that load continues down to a footing. R602.7.5 covers supports for headers, and a header sized correctly over a floor with nothing underneath it is a common and serious defect.

Girders and headers are the same table

The title says girder spans and header spans, and they are the same numbers. A header spans an opening in a wall; a girder carries a floor across a basement or crawl space. Structurally the table treats them alike because both are a beam in a bearing line carrying the conditions listed.

What differs is the support condition you pick. A girder under a floor system is usually one of the floor rows rather than the roof and ceiling row, and choosing the wrong row is the single biggest error available on this page.

Frequently asked questions

What size header do I need for a 6 foot opening?: For roof and ceiling only, on a 28 ft wide building at 30 psf ground snow, two 2x10s span 7 ft 3 in and cover it with two jack studs each end. Change any of those three conditions and the answer changes; the table has 549 live cells for a reason.
How many jack studs does a header need?: From the same cell as the span, between one and four. Where the table calls for one, footnote d permits an approved framing anchor fixed to the full-height king stud instead of a jack stud altogether.
Does header span depend on the species of lumber?: Not in this table. Footnote b pools Douglas fir-larch, hem-fir, southern pine and spruce-pine-fir into one set of values assuming #2 grade, which means the numbers are governed by the weakest of the four. That is unlike the joist and rafter tables, which do split by species.
What is building width in the header table?: The width of the building measured perpendicular to the ridge, because that is what sets how much roof lands on the wall. The table gives 20, 28 and 36 ft, and footnote c permits interpolation between them.
What if my building is wider than 36 feet?: There is no prescriptive answer. Footnote c permits interpolation between the widths shown and nothing permits extrapolating past the last one, so the header has to be designed. This calculator stops rather than extending the trend.
Can I use this table for an interior wall?: No. Table R602.7(1) is for exterior bearing walls. Interior bearing walls are Table R602.7(2) and the spans differ, because an interior wall generally carries floor and ceiling but not roof and snow.
Does the table cover LVL or engineered beams?: No. It is dimension lumber at #2 grade. LVL, glulam and PSL are proprietary products sized from the manufacturer's own published span tables, and reading them off a code table for sawn lumber is meaningless.
What is the difference between a girder and a header here?: For this table, nothing. It is titled girder spans and header spans and the values serve both. A header spans an opening in a wall, a girder carries a floor across a basement, and both are beams in a bearing line carrying the listed conditions.

Check these numbers yourself

IRC Table R602.7(1), girder and header spans for exterior bearing wallsFranklin Regional Council of Governments, reproducing the 2015 IRC pages 169 and 170. Used because codes.iccsafe.org returns HTTP 403. The scan has no text layer and was read cell by cell.
AWC Span Calculator and design valuesAmerican Wood Council. Where a member falls outside the prescriptive table, this is the design path.
IRC R602.7 HeadersUpCodes. The section text and the supports-for-headers requirement in R602.7.5. Confirm the edition it serves you.

How every figure here is verified: Sources & Method. Who builds this: About. Found something wrong? Tell us and it gets fixed or removed.

Figures on this page last checked against the source documents on 2026-09-08. Codes are amended locally; confirm against the edition your jurisdiction enforces.

Related calculators

2015 IRC values. Editions and local amendments differ, so confirm what your jurisdiction has adopted. This table is for exterior bearing walls in #2 dimension lumber only. Past a 36 ft building width or 70 psf ground snow there is no prescriptive answer and the header must be designed. Nothing here addresses what supports the header below.