Section properties for standard dressed (S4S) sawn lumber per the National Design Specification (NDS) Supplement, Table 1B. For every nominal size you get the actual dressed dimensions and the cross-section properties used in wood design: area (A), section modulus (S), and moment of inertia (I) about both axes.
Need to actually design the member? StructSuite uses these exact values to size beams, joists, and rafters per the NDS — open the free wood-beam designer.
How these are calculated
For a rectangular section of width b and depth d (strong axis bending about the X-X axis):
- Area: A = b × d
- Section modulus: Sxx = b × d² / 6
- Moment of inertia: Ixx = b × d³ / 12
- Weak-axis values (Syy, Iyy) swap b and d.
Section properties table (NDS Supplement Table 1B)
Boards
| Nominal size | Dressed size (b × d), in. | A (in.²) | Sxx (in.³) | Ixx (in.⁴) | Syy (in.³) | Iyy (in.⁴) |
|---|---|---|---|---|---|---|
| 1 × 3 | 3/4 × 2-1/2 | 1.875 | 0.781 | 0.977 | 0.234 | 0.088 |
| 1 × 4 | 3/4 × 3-1/2 | 2.625 | 1.531 | 2.680 | 0.328 | 0.123 |
| 1 x 6 | 3/4 × 5-1/2 | 4.125 | 3.781 | 10.40 | 0.516 | 0.193 |
| 1 × 8 | 3/4 × 7-1/4 | 5.438 | 6.570 | 23.82 | 0.680 | 0.255 |
| 1 x 10 | 3/4 × 9-1/4 | 6.938 | 10.70 | 49.47 | 0.867 | 0.325 |
| 1 x 12 | 3/4 × 11-1/4 | 8.438 | 15.82 | 88.99 | 1.055 | 0.396 |
Dimension Lumber & Decking
| Nominal size | Dressed size (b × d), in. | A (in.²) | Sxx (in.³) | Ixx (in.⁴) | Syy (in.³) | Iyy (in.⁴) |
|---|---|---|---|---|---|---|
| 2 x 3 | 1-1/2 × 2-1/2 | 3.750 | 1.560 | 1.953 | 0.938 | 0.703 |
| 2 × 4 | 1-1/2 × 3-1/2 | 5.250 | 3.060 | 5.359 | 1.313 | 0.984 |
| 2 × 5 | 1-1/2 × 4-1/2 | 6.750 | 5.060 | 11.39 | 1.688 | 1.266 |
| 2 x 6 | 1-1/2 × 5-1/2 | 8.250 | 7.560 | 20.80 | 2.063 | 1.547 |
| 2 × 8 | 1-1/2 × 7-1/4 | 10.88 | 13.14 | 47.63 | 2.719 | 2.039 |
| 2 x 10 | 1-1/2 × 9-1/4 | 13.88 | 21.39 | 98.93 | 3.469 | 2.602 |
| 2 x 12 | 1-1/2 × 11-1/4 | 16.88 | 31.64 | 178.0 | 4.219 | 3.164 |
| 2 x 14 | 1-1/2 × 13-1/4 | 19.88 | 43.89 | 290.8 | 4.969 | 3.727 |
| 3 x 4 | 2-1/2 × 3-1/2 | 8.750 | 5.100 | 8.932 | 3.646 | 4.557 |
| 3 × 5 | 2-1/2 × 4-1/2 | 11.25 | 8.440 | 18.98 | 4.688 | 5.859 |
| 3 x 6 | 2-1/2 × 5-1/2 | 13.75 | 12.60 | 34.66 | 5.729 | 7.161 |
| 3 × 8 | 2-1/2 × 7-1/4 | 18.13 | 21.90 | 79.39 | 7.552 | 9.440 |
| 3 x 10 | 2-1/2 × 9-1/4 | 23.13 | 35.65 | 164.9 | 9.635 | 12.04 |
| 3 x 12 | 2-1/2 × 11-1/4 | 28.13 | 52.73 | 296.6 | 11.72 | 14.65 |
| 3 x 14 | 2-1/2 × 13-1/4 | 33.13 | 73.15 | 484.6 | 13.80 | 17.25 |
| 3 x 16 | 2-1/2 × 15-1/4 | 38.13 | 96.90 | 738.9 | 15.89 | 19.86 |
| 4 x 4 | 3-1/2 × 3-1/2 | 12.25 | 7.150 | 12.51 | 7.146 | 12.51 |
| 4 × 5 | 3-1/2 × 4-1/2 | 15.75 | 11.81 | 26.58 | 9.188 | 16.08 |
| 4 × 6 | 3-1/2 × 5-1/2 | 19.25 | 17.65 | 48.53 | 11.23 | 19.65 |
| 4 x 8 | 3-1/2 × 7-1/4 | 25.38 | 30.66 | 111.1 | 14.80 | 25.90 |
| 4 x 10 | 3-1/2 × 9-1/4 | 32.38 | 49.91 | 230.8 | 18.89 | 33.05 |
| 4 x 12 | 3-1/2 × 11-1/4 | 39.38 | 73.83 | 415.3 | 22.97 | 40.20 |
| 4 x 14 | 3-1/2 × 13-1/4 | 46.38 | 102.4 | 678.5 | 27.05 | 47.34 |
| 4 x 16 | 3-1/2 × 15-1/4 | 53.38 | 135.7 | 1034 | 31.14 | 54.49 |
Posts & Timbers (5×5 in. and larger)
| Nominal size | Dressed size (b × d), in. | A (in.²) | Sxx (in.³) | Ixx (in.⁴) | Syy (in.³) | Iyy (in.⁴) |
|---|---|---|---|---|---|---|
| 5×5 | 4-1/2 × 4-1/2 | 20.25 | 15.19 | 34.17 | 15.19 | 34.17 |
| 6 × 6 | 5-1/2 × 5-1/2 | 30.25 | 27.73 | 76.26 | 27.73 | 76.26 |
| 6 × 8 | 5-1/2 × 7-1/2 | 41.25 | 51.56 | 193.4 | 37.81 | 104.0 |
| 8 x 8 | 7-1/2 × 7-1/2 | 56.25 | 70.31 | 263.7 | 70.31 | 263.7 |
| 8 x 10 | 7-1/2 × 9-1/2 | 71.25 | 112.8 | 535.9 | 89.06 | 334.0 |
| 10 x 10 | 9-1/2 × 9-1/2 | 90.25 | 142.9 | 678.8 | 142.9 | 678.8 |
| 10 x 12 | 9-1/2 × 11-1/2 | 109.3 | 209.4 | 1204 | 173.0 | 821.7 |
| 12 x 12 | 11-1/2 × 11-1/2 | 132.3 | 253.5 | 1458 | 253.5 | 1458 |
| 12 x 14 | 11-1/2 × 13-1/2 | 155.3 | 349.3 | 2358 | 297.6 | 1711 |
| 14 x 14 | 13-1/2 × 13-1/2 | 182.3 | 410.1 | 2768 | 410.1 | 2768 |
| 14 x 16 | 13-1/2 × 15-1/2 | 209.3 | 540.6 | 4189 | 470.8 | 3178 |
| 16 x 16 | 15-1/2 × 15-1/2 | 240.3 | 620.6 | 4810 | 620.6 | 4810 |
| 16 x 18 | 15-1/2 × 17-1/2 | 271.3 | 791.1 | 6923 | 700.7 | 5431 |
| 18 x 18 | 17-1/2 × 17-1/2 | 306.3 | 893.2 | 7816 | 893.2 | 7816 |
| 18 x 20 | 17-1/2 × 19-1/2 | 341.3 | 1109 | 10813 | 995.3 | 8709 |
| 20 x 20 | 19-1/2 × 19-1/2 | 380.3 | 1236 | 12049 | 1236 | 12049 |
| 20 x 22 | 19-1/2 × 21-1/2 | 419.3 | 1502 | 16150 | 1363 | 13285 |
| 22 x 22 | 21-1/2 × 21-1/2 | 462.3 | 1656 | 17806 | 1656 | 17806 |
| 22 x 24 | 21-1/2 × 23-1/2 | 505.3 | 1979 | 23252 | 1810 | 19463 |
| 24 x 24 | 23-1/2 × 23-1/2 | 552.3 | 2163 | 25415 | 2163 | 25415 |
Beams & Stringers
| Nominal size | Dressed size (b × d), in. | A (in.²) | Sxx (in.³) | Ixx (in.⁴) | Syy (in.³) | Iyy (in.⁴) |
|---|---|---|---|---|---|---|
| 6 x 10 | 5-1/2 × 9-1/2 | 52.25 | 82.73 | 393.0 | 47.90 | 131.7 |
| 6 x 12 | 5-1/2 × 11-1/2 | 63.25 | 121.2 | 697.1 | 57.98 | 159.4 |
| 6 x 14 | 5-1/2 × 13-1/2 | 74.25 | 167.1 | 1128 | 68.06 | 187.2 |
| 6 x 16 | 5-1/2 × 15-1/2 | 85.25 | 220.2 | 1707 | 78.15 | 214.9 |
| 6 x 18 | 5-1/2 × 17-1/2 | 96.25 | 280.7 | 2456 | 88.23 | 242.6 |
| 6 x 20 | 5-1/2 × 19-1/2 | 107.3 | 348.6 | 3398 | 98.31 | 270.4 |
| 6 x 22 | 5-1/2 × 21-1/2 | 118.3 | 423.7 | 4555 | 108.4 | 298.1 |
| 6 x 24 | 5-1/2 × 23-1/2 | 129.3 | 506.2 | 5948 | 118.5 | 325.8 |
| 8 x 12 | 7-1/2 × 11-1/2 | 86.30 | 165.3 | 950.5 | 107.8 | 404.3 |
| 8 x 14 | 7-1/2 × 13-1/2 | 101.3 | 227.8 | 1538 | 126.6 | 474.6 |
| 8 x 16 | 7-1/2 × 15-1/2 | 116.3 | 300.3 | 2327 | 145.3 | 544.9 |
| 8 x 18 | 7-1/2 × 17-1/2 | 131.3 | 382.8 | 3350 | 164.1 | 615.2 |
| 8 × 20 | 7-1/2 × 19-1/2 | 146.3 | 475.3 | 4634 | 182.8 | 685.5 |
| 8 x 22 | 7-1/2 × 21-1/2 | 161.3 | 577.8 | 6211 | 201.6 | 755.9 |
| 8 x 24 | 7-1/2 × 23-1/2 | 176.3 | 690.3 | 8111 | 220.3 | 826.2 |
| 10 x 14 | 9-1/2 × 13-1/2 | 128.3 | 288.6 | 1948 | 203.1 | 964.5 |
| 10 x 16 | 9-1/2 × 15-1/2 | 147.3 | 380.4 | 2948 | 233.1 | 1107 |
| 10 x 18 | 9-1/2 × 17-1/2 | 166.3 | 484.9 | 4243 | 263.2 | 1250 |
| 10 x 20 | 9-1/2 × 19-1/2 | 185.3 | 602.1 | 5870 | 293.3 | 1393 |
| 10 x 22 | 9-1/2 × 21-1/2 | 204.3 | 731.9 | 7868 | 323.4 | 1536 |
| 10 x 24 | 9-1/2 × 23-1/2 | 223.3 | 874.4 | 10274 | 353.5 | 1679 |
| 12 x 16 | 11-1/2 × 15-1/2 | 178.3 | 460.5 | 3569 | 341.6 | 1964 |
| 12 x 18 | 11-1/2 × 17-1/2 | 201.3 | 587.0 | 5136 | 385.7 | 2218 |
| 12 x 20 | 11-1/2 × 19-1/2 | 224.3 | 728.8 | 7106 | 429.8 | 2471 |
| 12 x 22 | 11-1/2 × 21-1/2 | 247.3 | 886.0 | 9524 | 473.9 | 2725 |
| 12 x 24 | 11-1/2 × 23-1/2 | 270.3 | 1058 | 12437 | 518.0 | 2978 |
| 14 x 18 | 13-1/2 × 17-1/2 | 236.3 | 689.1 | 6029 | 531.6 | 3588 |
| 14 x 20 | 13-1/2 × 19-1/2 | 263.3 | 855.6 | 8342 | 592.3 | 3998 |
| 14 x 22 | 13-1/2 × 21-1/2 | 290.3 | 1040 | 11181 | 653.1 | 4408 |
| 14 x 24 | 13-1/2 × 23-1/2 | 317.3 | 1243 | 14600 | 713.8 | 4818 |
| 16 x 20 | 15-1/2 × 19-1/2 | 302.3 | 982.3 | 9578 | 780.8 | 6051 |
| 16 x 22 | 15-1/2 × 21-1/2 | 333.3 | 1194 | 12837 | 860.9 | 6672 |
| 16 x 24 | 15-1/2 × 23-1/2 | 364.3 | 1427 | 16763 | 941.0 | 7293 |
| 18 x 22 | 17-1/2 × 21-1/2 | 376.3 | 1348 | 14493 | 1097 | 9602 |
| 18 x 24 | 17-1/2 × 23-1/2 | 411.3 | 1611 | 18926 | 1199 | 10495 |
| 20 x 24 | 19-1/2 × 23-1/2 | 458.3 | 1795 | 21089 | 1489 | 14521 |
Values per the NDS Supplement (National Design Specification for Wood Construction), Table 1B — Section Properties of Standard Dressed (S4S) Sawn Lumber. X-X is the strong (bending) axis; Y-Y is the weak axis.
Frequently asked questions
What is the actual (dressed) size of nominal lumber like a 2x4 or 2x10?
Standard dressed (S4S) lumber is smaller than its nominal name. A nominal 2x4 is actually 1-1/2 in. × 3-1/2 in., and a nominal 2x10 is actually 1-1/2 in. × 9-1/4 in. The table on this page lists the actual dressed size for every nominal size per the NDS Supplement Table 1B.
How do you calculate the section modulus and moment of inertia of a rectangular wood member?
For a rectangular section of width b and depth d: Area A = b × d, Section modulus S = b × d² / 6, and Moment of inertia I = b × d³ / 12. The strong-axis values (Sxx, Ixx) use the full depth d; the weak-axis values (Syy, Iyy) swap b and d.
What is the section modulus of a 2x10?
A dressed 2x10 (1-1/2 in. × 9-1/4 in.) has a strong-axis section modulus Sxx ≈ 21.39 in.³ and a moment of inertia Ixx ≈ 98.93 in.⁴. See the Dimension Lumber rows in the table for exact values.
Which standard do these lumber section properties come from?
These are the section properties of standard dressed (S4S) sawn lumber published in the National Design Specification (NDS) Supplement, Table 1B. They are the values used in U.S. wood design per the NDS.
Design with these properties in StructSuite
Size wood beams, floor joists, ceiling joists, and rafters per the NDS — free, in your browser.