Nominal and actual lumber sizes with section properties, plus UK and Australian sizes.
A 2×4 measures 1½ × 3½ in, not 2 × 4. The name is a nominal size, and the real board is smaller after drying and planing. The chart lists the actual size of common softwood lumber in inches and millimetres, with area and strength properties for design.
Minimum dressed dry sizes under American Softwood Lumber Standard PS 20, at 19% moisture or less. S and I are about the strong axis, with the wide face vertical. Metric figures are rounded.
| Nominal (in) | Actual (in) | Actual (mm) | Cross-Section Area (in²) | Section Modulus S (in³) | Moment of Inertia I (in⁴) |
|---|---|---|---|---|---|
| 1×2 | ¾ × 1½ | 19 × 38 | 1.13 | 0.28 | 0.21 |
| 1×3 | ¾ × 2½ | 19 × 64 | 1.88 | 0.78 | 0.98 |
| 1×4 | ¾ × 3½ | 19 × 89 | 2.63 | 1.53 | 2.68 |
| 1×6 | ¾ × 5½ | 19 × 140 | 4.13 | 3.78 | 10.40 |
| 1×8 | ¾ × 7¼ | 19 × 184 | 5.44 | 6.57 | 23.82 |
| 1×10 | ¾ × 9¼ | 19 × 235 | 6.94 | 10.70 | 49.47 |
| 1×12 | ¾ × 11¼ | 19 × 286 | 8.44 | 15.82 | 88.99 |
| 2×2 | 1½ × 1½ | 38 × 38 | 2.25 | 0.56 | 0.42 |
| 2×3 | 1½ × 2½ | 38 × 64 | 3.75 | 1.56 | 1.95 |
| 2×4 | 1½ × 3½ | 38 × 89 | 5.25 | 3.06 | 5.36 |
| 2×6 | 1½ × 5½ | 38 × 140 | 8.25 | 7.56 | 20.80 |
| 2×8 | 1½ × 7¼ | 38 × 184 | 10.88 | 13.14 | 47.63 |
| 2×10 | 1½ × 9¼ | 38 × 235 | 13.88 | 21.39 | 98.93 |
| 2×12 | 1½ × 11¼ | 38 × 286 | 16.88 | 31.64 | 177.98 |
| 2×14 | 1½ × 13¼ | 38 × 337 | 19.88 | 43.89 | 290.8 |
| 3×4 | 2½ × 3½ | 64 × 89 | 8.75 | 5.10 | 8.93 |
| 3×6 | 2½ × 5½ | 64 × 140 | 13.75 | 12.60 | 34.66 |
| 4×4 | 3½ × 3½ | 89 × 89 | 12.25 | 7.15 | 12.51 |
| 4×6 | 3½ × 5½ | 89 × 140 | 19.25 | 17.65 | 48.53 |
| 4×8 | 3½ × 7¼ | 89 × 184 | 25.38 | 30.66 | 111.15 |
| 4×10 | 3½ × 9¼ | 89 × 235 | 32.38 | 49.91 | 230.84 |
| 4×12 | 3½ × 11¼ | 89 × 286 | 39.38 | 73.83 | 415.28 |
| 4×14 | 3½ × 13¼ | 89 × 337 | 46.38 | 102.4 | 678.5 |
| 6×6 | 5½ × 5½ | 140 × 140 | 30.25 | 27.73 | 76.26 |
| 6×8 | 5½ × 7½ | 140 × 191 | 41.25 | 51.56 | 193.36 |
| 8×8 | 7½ × 7½ | 191 × 191 | 56.25 | 70.31 | 263.67 |
26 rows
| Nominal | Actual, dry | Taken off |
|---|---|---|
| 1 in | ¾ in | ¼ in |
| 2, 3, 4, 6 in | 1½, 2½, 3½, 5½ in | ½ in |
| 8, 10, 12, 14 in | 7¼, 9¼, 11¼, 13¼ in | ¾ in |
The rule does not cover every product, but it gets you the common sizes without the chart.
PS 20 lists two sets of minimum sizes. Dry means 19% moisture or less. Green is above that, and it is cut larger to allow for shrinkage.
| Nominal | Dry | Green |
|---|---|---|
| 2 in | 1½ in | 1 9/16 in |
| 4 in | 3½ in | 3 9/16 in |
| 8 in | 7¼ in | 7½ in |
| 12 in | 11¼ in | 11½ in |
Large timbers, 5 in and up, are usually sold green, so a 6×6 is 5½ × 5½ in. Hardwood lumber uses a different system, sold in quarters of an inch of rough thickness.
Under the US uniform method-of-sale rule, a seller who labels lumber by nominal size must also show the actual or minimum dressed size.
Bending strength depends on section modulus, S = b × h² ÷ 6. Take a 2×10:
| Calculated with | S (in³) | I (in⁴) |
|---|---|---|
| Nominal 2 × 10 | 33.33 | 166.67 |
| Actual 1½ × 9¼ | 21.39 | 98.93 |
Nominal sizes overstate S by 56% and stiffness by 68%. Always use actual sizes. Orientation matters even more: laid flat, the same 2×10 has S = 3.47 in³, about one sixth of its strength on edge. That is why joists stand on edge.
For a beam check, see the beam deflection calculator and what a bending moment is. The table gives geometry only. Allowable stresses depend on species and grade, so size structural members from your span tables or an engineer.
Canada uses the same sizes as the US. Other markets do not, so check before you copy a design.
| Market | Common name | Actual size |
|---|---|---|
| UK | CLS "4 × 2" (50 × 100) | 38 × 89 mm |
| UK | Regularised C16 | 47 × 100 mm |
| Australia | MGP10 pine | 90 × 45 mm |
| Australia | MGP10 pine | 140 × 45 mm |
These come from retailer listings, so confirm the grade and size with your supplier.
By O.E. — Partner, chairman of the board and CEO of a metal products manufacturer for 21 years; the company exports to 45 countries.
Drafted with AI assistance; calculations checked against primary sources and tested with the site's own code. About FlowUtil
Last reviewed
Classification: Standard nominal vs actual dimensions
Sources
PS 20 — American Softwood Lumber Standard
NIST; administered by the American Lumber Standard Committee
Handbook 130, Section 2.10 — Uniform Method of Sale, softwood lumber
NIST
Nominal vs. Actual Lumber Sizes
Southern Pine Inspection Bureau
Wood Handbook — specific gravity
USDA Forest Products Laboratory
Dimensional lumber is sold by nominal size (e.g. 2×4) but the actual surfaced (S4S) size is smaller (e.g. 1½×3½ in) due to drying and planing. The table lists both. Full-sawn (rough) lumber is closer to the nominal size. Metric equivalents are shown for regions using millimetres.
Softwood lumber is sawn, dried and surfaced (planed) to the standard dressed size. The difference is ¼ in on 1 in stock, ½ in up to 6 in, and ¾ in on 8 in and wider. The table maps nominal to actual for the common dimensional sizes (2×4 through 2×12 and larger timbers).
Classification: Stable (mature standard)
Nominal-to-actual sizing has been stable for decades under the ALSC softwood standards. Confirm the actual size for the species and surfacing specified.
Nominal and actual dimensions in inches; metric equivalents in millimetres.
Go deeper with FlowUtil guides that explain the concepts behind this reference table.
Browse Knowledge Library