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A header carries the wall, roof and any floors above a door or window opening down to the jack studs at each side. The 2021 International Residential Code lists the maximum span of sawn-lumber headers in exterior bearing walls in Table R602.7(1), for No. 2 Douglas fir-larch, hem-fir, southern pine and spruce-pine-fir, by what the wall supports (roof and ceiling only, or one or two center-bearing or clear-span floors as well), the ground snow load (30, 50 or 70 psf) and the building width measured across the ridge (12, 24 or 36 ft), together with NJ, the jack studs needed at each end. For an exterior wall carrying only the roof and ceiling at 30 psf, a double 2x8 spans 7 ft 7 in, 5 ft 9 in and 4 ft 10 in on 12, 24 and 36 ft wide buildings, a double 2x10 9 ft 0 in, 6 ft 10 in and 5 ft 9 in, and a double 2x12 10 ft 7 in, 8 ft 1 in and 6 ft 10 in. Where cripple studs bear on top of the header, note f cuts the 2x8 to 2x12 spans to 70%. Enter the rough opening, building width, snow load and floors above and the Header Span Calculator picks the smallest header, the jack studs and the header length: a 6 ft opening on a 24 ft wide house needs a double 2x10 with two jacks each end, 78 in long.
Maximum header spans for exterior bearing walls from 2021 IRC Table R602.7(1): No. 2 Douglas fir-larch, hem-fir, southern pine and spruce-pine-fir. Building width is measured perpendicular to the ridge (note c); the number in brackets is NJ, the jack studs required at each end (note d). Use 30 psf where the ground snow load is less and the roof live load is 20 psf or less (note e). Spans assume the top of the header is laterally braced; otherwise 2x8, 2x10 and 2x12 spans × 0.70 (note f).
| Header | 12 ft wide | 24 ft wide | 36 ft wide |
|---|---|---|---|
| 1-2x6 | 4 ft (1) | 3 ft 1 in (2) | 2 ft 7 in (2) |
| 1-2x8 | 5 ft 1 in (2) | 3 ft 11 in (2) | 3 ft 3 in (2) |
| 1-2x10 | 6 ft (2) | 4 ft 8 in (2) | 3 ft 11 in (2) |
| 1-2x12 | 7 ft 1 in (2) | 5 ft 5 in (2) | 4 ft 7 in (3) |
| 2-2x4 | 4 ft (1) | 3 ft 1 in (1) | 2 ft 7 in (1) |
| 2-2x6 | 6 ft (1) | 4 ft 7 in (1) | 3 ft 10 in (1) |
| 2-2x8 | 7 ft 7 in (1) | 5 ft 9 in (1) | 4 ft 10 in (2) |
| 2-2x10 | 9 ft (1) | 6 ft 10 in (2) | 5 ft 9 in (2) |
| 2-2x12 | 10 ft 7 in (2) | 8 ft 1 in (2) | 6 ft 10 in (2) |
| 3-2x8 | 9 ft 5 in (1) | 7 ft 3 in (1) | 6 ft 1 in (1) |
| 3-2x10 | 11 ft 3 in (1) | 8 ft 7 in (1) | 7 ft 3 in (2) |
| 3-2x12 | 13 ft 2 in (1) | 10 ft 1 in (2) | 8 ft 6 in (2) |
| 4-2x8 | 10 ft 11 in (1) | 8 ft 4 in (1) | 7 ft (1) |
| 4-2x10 | 12 ft 11 in (1) | 9 ft 11 in (1) | 8 ft 4 in (1) |
| 4-2x12 | 15 ft 3 in (1) | 11 ft 8 in (1) | 9 ft 10 in (2) |
| Header | 12 ft wide | 24 ft wide | 36 ft wide |
|---|---|---|---|
| 1-2x6 | 3 ft 3 in (1) | 2 ft 7 in (2) | 2 ft 2 in (2) |
| 1-2x8 | 4 ft 1 in (2) | 3 ft 3 in (2) | 2 ft 9 in (2) |
| 1-2x10 | 4 ft 11 in (2) | 3 ft 10 in (2) | 3 ft 3 in (3) |
| 1-2x12 | 5 ft 9 in (2) | 4 ft 6 in (3) | 3 ft 10 in (3) |
| 2-2x4 | 3 ft 3 in (1) | 2 ft 6 in (1) | 2 ft 2 in (1) |
| 2-2x6 | 4 ft 10 in (1) | 3 ft 9 in (1) | 3 ft 3 in (2) |
| 2-2x8 | 6 ft 1 in (1) | 4 ft 10 in (2) | 4 ft 1 in (2) |
| 2-2x10 | 7 ft 3 in (2) | 5 ft 8 in (2) | 4 ft 10 in (2) |
| 2-2x12 | 8 ft 6 in (2) | 6 ft 8 in (2) | 5 ft 8 in (2) |
| 3-2x8 | 7 ft 8 in (1) | 6 ft (1) | 5 ft 1 in (2) |
| 3-2x10 | 9 ft 1 in (1) | 7 ft 2 in (2) | 6 ft 1 in (2) |
| 3-2x12 | 10 ft 8 in (2) | 8 ft 5 in (2) | 7 ft 2 in (2) |
| 4-2x8 | 8 ft 10 in (1) | 6 ft 11 in (1) | 5 ft 11 in (1) |
| 4-2x10 | 10 ft 6 in (1) | 8 ft 3 in (2) | 7 ft (2) |
| 4-2x12 | 12 ft 4 in (1) | 9 ft 8 in (2) | 8 ft 3 in (2) |
On an exterior wall carrying only the roof and ceiling of a 24 ft wide house with 30 psf ground snow, 2021 IRC Table R602.7(1) gives a double 2x8 5 ft 9 in and a double 2x10 6 ft 10 in, so a 72 in rough opening needs a double 2x10 with two jack studs at each end. On a 12 ft wide building a double 2x8 (7 ft 7 in) is enough.
Under the roof and ceiling only, at 30 psf ground snow: 9 ft 0 in for a 12 ft wide building, 6 ft 10 in at 24 ft and 5 ft 9 in at 36 ft. With one center-bearing floor above, those drop to 7 ft 3 in, 5 ft 8 in and 4 ft 10 in (IRC Table R602.7(1), No. 2 Douglas fir-larch, hem-fir, southern pine or spruce-pine-fir).
The NJ column of Table R602.7(1) gives the jack studs at each end — one to four depending on size, span and load. Where it is one, the IRC lets you use an approved framing anchor fixed to the full-height stud instead (note d). Each jack stud adds 1 1/2 in to the header length at each end.
The building width is measured perpendicular to the ridge — the distance the roof and floor framing carry load to the wall (note c). Widths between 12, 24 and 36 ft may be interpolated; this calculator rounds up to the next column, which is the conservative choice.
The tabulated spans assume the top of the header is laterally braced by perpendicular framing. Where it is not — for example cripple studs bearing on the header — spans of 2x8, 2x10 and 2x12 headers are multiplied by 0.70, or the header must be designed (note f).
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