A 2×4 is not 2 by 4 inches. Softwood lumber is named by its nominal size, and sold at a smaller dressed (actual) size after it has been dried and planed. The charts below give the standard sizes from the American Softwood Lumber Standard, as published in Table 6-6 of the USDA Forest Products Laboratory Wood Handbook, for boards, dimension lumber and timbers, both dry (19% moisture content or less) and green, plus the standard hardwood thicknesses from Table 6-4. Below them is a table of the common framing sizes with their real cross-section and weight, worked out from the Handbook densities.
Thickness: nominal vs actual
| Item | Nominal (in) | Actual dry (in) | Actual green (in) |
|---|---|---|---|
| Boards | 1 | 3/4 (19 mm) | 25/32 (20 mm) |
| 1-1/4 | 1 (25 mm) | 1-1/32 (26 mm) | |
| 1-1/2 | 1-1/4 (32 mm) | 1-9/32 (33 mm) | |
| Dimension | 2 | 1-1/2 (38 mm) | 1-9/16 (40 mm) |
| 2-1/2 | 2 (51 mm) | 2-1/16 (52 mm) | |
| 3 | 2-1/2 (64 mm) | 2-9/16 (65 mm) | |
| 3-1/2 | 3 (76 mm) | 3-1/16 (78 mm) | |
| 4 | 3-1/2 (89 mm) | 3-9/16 (90 mm) | |
| 4-1/2 | 4 (102 mm) | 4-1/16 (103 mm) |
Width: nominal vs actual
| Nominal width (in) | Actual dry (in) | Actual green (in) |
|---|---|---|
| 2 | 1-1/2 (38 mm) | 1-9/16 (40 mm) |
| 3 | 2-1/2 (64 mm) | 2-9/16 (65 mm) |
| 4 | 3-1/2 (89 mm) | 3-9/16 (90 mm) |
| 5 | 4-1/2 (114 mm) | 4-5/8 (117 mm) |
| 6 | 5-1/2 (140 mm) | 5-5/8 (143 mm) |
| 7 | 6-1/2 (165 mm) | 6-5/8 (168 mm) |
| 8 | 7-1/4 (184 mm) | 7-1/2 (190 mm) |
| 9 | 8-1/4 (210 mm) | 8-1/2 (216 mm) |
| 10 | 9-1/4 (235 mm) | 9-1/2 (241 mm) |
| 11 | 10-1/4 (260 mm) | 10-1/2 (267 mm) |
| 12 | 11-1/4 (286 mm) | 11-1/2 (292 mm) |
| 14 | 13-1/4 (337 mm) | 13-1/2 (343 mm) |
| 16 | 15-1/4 (387 mm) | 15-1/2 (394 mm) |
Timbers (5 in and larger)
Timbers follow a rule instead of a list. Surfaced dry, a nominal 5 or 6 in face is 1/2 in under nominal, 7 to 15 in is 3/4 in under, and 16 in and over is 1 in under. Surfaced green, every timber size is 1/2 in under nominal, so a green 6×6 is 5-1/2 by 5-1/2 in and an 8×8 is 7-1/2 by 7-1/2 in (Table 6-6).
Common framing sizes: real area and weight
| Size | Actual (dry) | Metric | Area (in²) | Board ft per ft | Lb per 8 ft, Douglas-fir | Southern pine (loblolly) | Eastern white pine |
|---|---|---|---|---|---|---|---|
| 2×4 | 1-1/2 x 3-1/2 in | 38 x 89 mm | 5.25 | 0.67 | 9.8 | 10.4 | 7.1 |
| 2×6 | 1-1/2 x 5-1/2 in | 38 x 140 mm | 8.25 | 1.00 | 15.4 | 16.4 | 11.2 |
| 2×8 | 1-1/2 x 7-1/4 in | 38 x 184 mm | 10.88 | 1.33 | 20.3 | 21.6 | 14.8 |
| 2×10 | 1-1/2 x 9-1/4 in | 38 x 235 mm | 13.88 | 1.67 | 25.9 | 27.5 | 18.9 |
| 2×12 | 1-1/2 x 11-1/4 in | 38 x 286 mm | 16.88 | 2.00 | 31.5 | 33.5 | 23.0 |
| 4×4 | 3-1/2 x 3-1/2 in | 89 x 89 mm | 12.25 | 1.33 | 22.9 | 24.3 | 16.7 |
| 4×6 | 3-1/2 x 5-1/2 in | 89 x 140 mm | 19.25 | 2.00 | 35.9 | 38.2 | 26.2 |
Hardwood thickness: quarters, rough and surfaced
| Quarter | Rough (in) | Surfaced two sides, S2S (in) |
|---|---|---|
| 3/8 | 3/16 | |
| 1/2 | 5/16 | |
| 5/8 | 7/16 | |
| 3/4 | 9/16 | |
| 4/4 | 1 | 13/16 |
| 5/4 | 1-1/4 | 1-1/16 |
| 6/4 | 1-1/2 | 1-5/16 |
| 7/4 | 1-3/4 | 1-1/2 |
| 8/4 | 2 | 1-3/4 |
| 10/4 | 2-1/2 | 2-1/4 |
| 12/4 | 3 | 2-3/4 |
| 14/4 | 3-1/2 | 3-1/4 |
| 16/4 | 4 | 3-3/4 |
Hardwood is usually bought rough and in random widths and lengths, and you lose more to planing than the S2S size suggests if the board is cupped or twisted. To finish a 3/4 in tabletop you normally buy 4/4 (1 in rough) stock; for 1 in finished parts, buy 5/4.
Worked examples
Wall thickness. A wall framed with 2×4 studs is 3-1/2 in thick, not 4. Add 1/2 in drywall on each side and the finished wall is 4-1/2 in. With 2×6 studs it is 5-1/2 + 1 = 6-1/2 in.
Built-up posts and beams. Three 2x10s nailed together are 3 x 1-1/2 = 4-1/2 in wide and 9-1/4 in deep. A “4×4” post is 3-1/2 in square, so a post base sized for a nominal 4×4 will not fit a 4-1/2 in built-up post.
How much wood you actually get. A 2×4 has 5.25 in² of cross-section against a nominal 8 in², or 66%. A 2×12 has 16.88 in² against 24 in² (70%). That is why lumber is priced per board foot on nominal size but your cut list must use actual sizes.
Common mistakes
- Designing with nominal sizes. Shelving, cabinets and furniture plans should always use the actual dimensions in the chart; a shelf for “two 1x12s” is 22-1/2 in, not 24.
- Assuming every board of a size is identical. These are minimum dressed sizes. Green lumber, rough-sawn cedar and timbers can be noticeably larger, and boards shrink further as they dry in your house (see the wood movement calculator).
- Mixing dry and green framing. A green 2×10 is 9-1/2 in deep, a dry one 9-1/4 in. Joists from different batches can leave a 1/4 in step in a floor or deck.
- Using the softwood rules for hardwood. Hardwood is sold rough in quarters; there is no “1×6 oak” standard, although some stores sell surfaced hardwood boards in softwood-style nominal sizes.
Frequently asked questions
What are the actual dimensions of a 2×4?
1-1/2 by 3-1/2 inches (38 by 89 mm) when dry, or 1-9/16 by 3-9/16 in if surfaced green. Its cross-section is 5.25 square inches, about 66% of the nominal 8.
Why is a 2×4 not 2 by 4 inches?
The nominal size is roughly the rough-sawn size before drying and planing. Drying shrinks the wood and surfacing removes more, and the American Softwood Lumber Standard sets the minimum dressed sizes that are sold.
What does 4/4 mean for hardwood?
Hardwood is sold rough by thickness in quarter inches: 4/4 is 1 in rough, 8/4 is 2 in. Surfaced on two sides, the Handbook’s standard sizes are 13/16 in for 4/4 and 1-3/4 in for 8/4.
Do I calculate board feet with nominal or actual size?
Softwood lumber is sold by board feet on the nominal size: a 2×4 8 ft long is 2 x 4 x 8 / 12 = 5.33 board feet. Hardwood is measured on the rough size as sawn.
Sources
- USDA Forest Products Laboratory. Wood Handbook: Wood as an Engineering Material. FPL-GTR-190, 2010. Chapter 6, Table 6-4 (hardwood thicknesses) and Table 6-6 (American Standard Lumber sizes for yard and structural lumber). Chapter 4 densities for the weight column.
- American Softwood Lumber Standard, Voluntary Product Standard PS 20 (NIST), the source of the sizes reproduced in Handbook Table 6-6.
Last reviewed: 24 October 2026. Related: lumber grades explained, board foot chart, board foot calculator, lumber cost calculator, cut list optimizer, the wood species database and the Janka hardness chart. Spotted an error? Please let us know.