Header size calculator: what size header for a door, window or garage opening

Exterior wall, roof and ceiling only, 24 ft wide, 30 psf ground snow: Table R602.7(1) gives a double 2x10 (6′ 10″, two jack studs each end) or a triple 2x8 (7′ 3″, one jack). Add a clear-span floor above and the double 2x10 no longer reaches 6 ft; on a 36 ft house with two clear-span floors nothing in the table does. On an interior wall under one floor at 24 ft, a triple 2x10 (8′ 1″) is the shallowest that works. Enter your own wall and width; none of these is the answer for a house you have not looked up.

Between 9 ft and 3 ft 2 in, depending on the cell. The longest span is 9′ 0″ on a 12 ft wide building with roof and ceiling only at 30 psf snow; at 24 ft the same header spans 6′ 10″, 5′ 11″ and 5′ 3″ as the ground snow load goes 30, 50, 70 psf; at 36 ft with two clear-span floors above it spans 3′ 2″. On an interior bearing wall, 24 ft wide, it spans 6′ 6″ under one floor and 4′ 4″ under two. Multiply any 2x10 span by 0.70 if cripple studs bear on the header.

The number in the NJ column of the cell you read the span from, at each end. It ranges from 1 to 4 in the exterior table and is 2 or more in 538 of the 675 cells, so two jack studs each end is the normal case for an exterior header and one is the exception. Where NJ is 1, note d lets an approved framing anchor fastened to the full-height stud and the header replace the jack stud. A deeper header can need fewer jacks than a shallower one over the same opening, because NJ follows the cell, not the span.

Table R602.7.5 sets the minimum full-height studs at each end of a header in an exterior wall by header span and wind speed: 1 for a 4 ft span, 2 for 6 and 8 ft, 3 for 10 to 14 ft and 4 for 16 and 18 ft where the ultimate design wind speed is under 140 mph in Exposure B or under 130 mph in Exposure C; 1, 1, 1, 2, 2, 2, 2, 2 at 115 mph or less in Exposure B. Use the count for the next larger span listed, and add the jack studs from the header table.

No dimensional lumber header in Table R602.7(1) reaches 16 ft: the longest span it prints is 15 ft 3 in, and that is a 4-ply 2x12 on a 12 ft wide building with only roof above. A 16 ft door in a bearing wall needs an engineered header, LVL, PSL, glulam or steel, sized for the actual load. If the door is in a gable-end wall it usually carries only the wall above the opening and is a nonbearing header, which is a different rule. Either way the wall beside a wide garage opening still needs its bracing under R602.10.

Note c says only that building width is measured perpendicular to the ridge, and this calculator takes that full width, so a 26 ft house is read in the 36 ft column. Plan reviewers sometimes accept a reduced width for an exterior header where the roof and floor above are supported mid-house, treating the header as carrying half the building, but that is a local judgement and not a rule printed in the table. The clear-span versus centre-bearing choice in the tool handles the floor joists; it does not change the width you enter.

No. Section R602.7.4 says load-bearing headers are not required in nonbearing walls, and allows a single flat 2x4 for openings up to 8 ft where the nailing surface above is within 24 in. Which walls are nonbearing, and the rim-board and box-header options, are in the header code guide.

Yes, in an exterior bearing wall. Table R602.7(1) has single-ply rows from 1-2x6 to 1-2x12, and Section R602.7.1 says how to frame one: a single 2x member on edge with a flat 2x plate, at least as wide as the studs, face-nailed above and below it with 10d box nails at 12 in on centre. A single 2x6 spans as far as a double 2x4 in every cell, but it needs an extra jack stud in 42 of those 45 cells, because the bearing is narrower. The interior table has no single-ply rows, so an interior header starts at a double 2x4.

In span terms, yes, in every cell the tables print: the triple 2x8 out-spans the double 2x10 in all 51 exterior and interior cells where both appear, by a few inches to a foot, and it usually needs one fewer jack stud. The trade-off is thickness. Three 2x8s are 4½ in and belong in a 2x6 wall; in a 2x4 wall they stand an inch proud. That is why the calculator shows both the shallowest header and the one with the fewest boards: for a 6 ft opening at the defaults they are the triple 2x8 and the double 2x10.

The spacer brings a 3 in double header out to the 3½ in stud thickness; it adds nothing to the table span, and the plies must match. The full answer, with the nailing schedule for a built-up member, is on the beam span calculator.

Yes, when they are the only thing above it. Note f to Table R602.7(1) and note e to R602.7(2) assume the top of the header is laterally braced by perpendicular framing; where it is not, and cripple studs bearing on the header are the example the code gives, spans for 2x8, 2x10 and 2x12 headers are multiplied by 0.70, or the header is designed. A double 2x10 that spans 6′ 10″ braced spans 4′ 9″ unbraced. A header set tight under the top plate is braced by it. Use the toggle in the calculator to apply the factor.

The header span in the table is the clear distance between the jack studs, and for a framed opening that is the rough opening width. It is not the door or window size, which is smaller by the shim space and the jamb, usually about 2 in, and it is not the header length, which is longer by the two jack studs it bears on, 1½ in each. Enter the rough opening in the calculator. In the second mode, compare the span it returns with your measured rough opening: if the opening is wider, the header does not meet the table.

Not in these tables. Note b bases every span on No.2 Douglas fir-larch, hem-fir, Southern pine and spruce-pine-fir together, so one value serves all four and a better grade earns no extra span here. Why the other span tables do split by species is on the beam span calculator.

No. Laminated veneer lumber, parallel strand lumber and glulam are sized from the manufacturer's tables or by an engineer, not from R602.7. What an LVL supplier needs from you, and how their tables compare, is in beam span and size questions.

The same table cell as a 2x4 wall; the wall thickness changes what fits, not what spans. A 2x6 wall takes a 3-ply header with two spacers, so the triple rows of the chart become usable and often save a size in depth. For a 3 ft exterior door at the tool's defaults the chart gives a double 2x4 (3′ 1″, one jack), a double 2x6 (4′ 7″) or a double 2x8 (5′ 9″), built with two spacers in a 2x6 wall or as a single 2x on edge with flat plates per R602.7.1.

The ground snow load for the site, from Figure R301.2(3) or the building department, rounded up to the 30, 50 or 70 psf column. Note e says to use the 30 psf column where ground snow is less than 30 psf and the roof live load is 20 psf or less, and 30 psf is the tool's default. Above 70 psf Section R301.2.3 requires an engineered design and the table stops. Interior headers and porch floor headers carry no roof, so the input disappears for them.

In an exterior bearing wall with roof and ceiling only, 24 ft wide, 30 psf snow, a 38 in rough opening takes a double 2x4 (3′ 1″, one jack stud each end), the smallest header in the table. A double 2x6 reaches 4′ 7″ and a double 2x8 5′ 9″ in the same cell, and framers often use one of those so the header lands under the top plate without cripples. Add one centre-bearing floor above and the double 2x4 drops to 2′ 6″ at 24 ft; in a nonbearing wall no sized header is needed at all.