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The Stud Calculator counts the framing for one wall. Studs on layout are the wall length in inches divided by the spacing, rounded up, plus one for the end. It adds 2 studs for each corner or wall intersection, and at each opening the jack studs under the header plus the full-height (king) studs the International Residential Code requires at each end: IRC Table R602.7.5 sets 1 per end for a 4 ft header, 2 for 6–8 ft and 3 for 10–14 ft in exterior walls below 140 mph in Exposure B, and 1 up to 8 ft and 2 up to 18 ft where the wind speed is 115 mph or less. An allowance covers crooked or split studs. Plates are a single bottom plate (R602.3.4) and a double top plate with end joints offset at least 24 in (R602.3.2) — three times the wall length. It then checks IRC Table R602.3(5): 2 × 4 studs may be 24 in apart under a roof and ceiling only but 16 in with a floor above, 2 × 6 studs 24 in with one floor and 16 in with two, and bearing studs are limited to 10 ft unsupported. A 20 ft exterior wall at 16 in on center has 16 studs; with two corners, one 3 ft window and 10% extra it takes 27, plus six 10 ft plates.
Studs = wall length in inches ÷ spacing, rounded up, + 1. Add studs for corners and, at each opening, jack studs and the full-height studs of IRC Table R602.7.5. Plates are one bottom plate (IRC R602.3.4) and a double top plate with end joints offset at least 24 in (R602.3.2).
| Stud | Bearing height | Roof + ceiling only | One floor + roof | Two floors + roof | Nonbearing height | Nonbearing spacing |
|---|---|---|---|---|---|---|
| 2 × 3 | — | not permitted | not permitted | not permitted | 10 ft | 16 in |
| 2 × 4 | 10 ft | 24 in | 16 in | not permitted | 14 ft | 24 in |
| 3 × 4 | 10 ft | 24 in | 24 in | 16 in | 14 ft | 24 in |
| 2 × 5 | 10 ft | 24 in | 24 in | not permitted | 16 ft | 24 in |
| 2 × 6 | 10 ft | 24 in | 24 in | 16 in | 20 ft | 24 in |
| Header span up to | < 140 mph Exp. B or < 130 mph Exp. C | ≤ 115 mph Exposure B |
|---|---|---|
| 4 ft | 1 | 1 |
| 6 ft | 2 | 1 |
| 8 ft | 2 | 1 |
| 10 ft | 3 | 2 |
| 12 ft | 3 | 2 |
| 14 ft | 3 | 2 |
| 16 ft | 4 | 2 |
| 18 ft | 4 | 2 |
| Wall | 12 in o.c. | 16 in o.c. | 24 in o.c. |
|---|---|---|---|
| 8 ft | 9 | 7 | 5 |
| 10 ft | 11 | 9 | 6 |
| 12 ft | 13 | 10 | 7 |
| 16 ft | 17 | 13 | 9 |
| 20 ft | 21 | 16 | 11 |
| 24 ft | 25 | 19 | 13 |
| 30 ft | 31 | 24 | 16 |
| 40 ft | 41 | 31 | 21 |
Divide the wall length in inches by the stud spacing, round up and add one for the end stud. Then add studs for corners, and king and jack studs at each opening. A 20 ft wall at 16 in on center has 16 studs; with two corners, one 3 ft window and 10% extra it needs 27.
At 16 in on center a 10 ft (120 in) wall needs 120 ÷ 16 = 7.5, rounded up to 8 spaces, plus 1 = 9 studs before corners and openings. At 24 in on center it needs 6.
Often. IRC Table R602.3(5) allows 2 × 4 studs at 24 in on center in a bearing wall that carries only a roof and ceiling, and in nonbearing walls, but limits them to 16 in when the wall also carries a floor. 2 × 6 studs can be 24 in apart with one floor above and 16 in with two. Bearing studs are limited to 10 ft of unsupported height.
IRC R602.3.2 caps wood stud walls with a double top plate that overlaps at corners and bearing intersections, with end joints offset at least 24 in. Add a single bottom plate (R602.3.4) and a wall needs three times its length in plate lumber.
IRC Table R602.7.5 sets the minimum full-height studs at each end of a header in an exterior wall: 1 for a 4 ft header, 2 for 6–8 ft and 3 for 10–14 ft where the wind speed is under 140 mph in Exposure B, and fewer (1 up to 8 ft, 2 up to 18 ft) at 115 mph or less. Each header also sits on jack studs per Table R602.7(1).
Sizing the header over the opening? The header span chart gives the IRC header and its jack studs.
Need the whole roof at once? The free roofing calculator works out roof area, squares, shingle bundles, underlayment, drip edge, ridge cap and installed cost from one set of measurements.