Dimensional lumber is cut to a specific length, width, and depth. However, there is a difference between the nominal size (what the lumber is referred to) and the actual size. The tables below provide both the nominal and actual lumber dimensions for many common North American lumber sizes.
Softwood Lumber Dimensions
Softwood lumber is generally used for framing walls and floors. In the United States, softwood lumber is governed by the National Institute of Standards American Softwood Lumber Standard (PS 20).
North American Standard 1-by Lumber
| NOMINAL SIZE (INCHES) | ACTUAL SIZE (INCHES) | ACTUAL SIZE (MM) |
|---|---|---|
| 1 x 2 | 3/4 x 1 1/2 | 19 x 38 |
| 1 x 3 | 3/4 x 2 1/2 | 19 x 64 |
| 1 x 4 | 3/4 x 3 1/2 | 19 x 89 |
| 1 x 6 | 3/4 x 5 1/2 | 19 x 140 |
| 1 x 8 | 3/4 x 7 1/4 | 19 x 184 |
| 1 x 10 | 3/4 x 9 1/4 | 19 x 235 |
| 1 x 12 | 3/4 x 11 1/4 | 19 x 286 |
North American Standard 2-by Lumber
| NOMINAL SIZE (INCHES) | ACTUAL SIZE (INCHES) | ACTUAL SIZE (MM) |
|---|---|---|
| 2 x 2 | 1 1/2 x 1 1/2 | 38 x 38 |
| 2 x 3 | 1 1/2 x 2 1/2 | 38 x 64 |
| 2 x 4 | 1 1/2 x 3 1/2 | 38 x 89 |
| 2 x 6 | 1 1/2 x 5 1/2 | 38 x 140 |
| 2 x 8 | 1 1/2 x 7 1/4 | 38 x 184 |
| 2 x 10 | 1 1/2 x 9 1/4 | 38 x 235 |
| 2 x 12 | 1 1/2 x 11 1/4 | 38 x 286 |
North American Standard 4-by Lumber
| NOMINAL SIZE (INCHES) | ACTUAL SIZE (INCHES) | ACTUAL SIZE (MM) |
|---|---|---|
| 4 x 4 | 3 1/2 x 3 1/2 | 89 x 89 |
| 4 x 6 | 3 1/2 x 5 1/2 | 89 x 140 |
| 4 x 8 | 3 1/2 x 7 1/4 | 89 x 184 |
| 4 x 10 | 3 1/2 x 9 1/4 | 89 x 235 |
| 4 x 12 | 3 1/2 x 11 1/4 | 89 x 286 |
Softwood Timber Dimensions
Softwood lumber that has a thickness over 5" is called timber.
While NIST Publication PS20 indicates that nominal 7" to 15" thick timbers should have 3/4" removed for a finished dimension (e.g. a nominal 8x8 timber has a minimum finished size of 7.25" x 7.25"), most timbers over 7" are finished with 1/2" removed.
North American Standard 6-by Timber (Surfaced 4 Sides, S4S)
| NOMINAL SIZE (INCHES) | ACTUAL SIZE (INCHES) | ACTUAL SIZE (MM) |
|---|---|---|
| 6 x 6 | 5 1/2 x 5 1/2 | 140 x 140 |
| 6 x 8 | 5 1/2 x 7 1/2 | 140 x 191 |
| 6 x 10 | 5 1/2 x 9 1/2 | 140 x 241 |
| 6 x 12 | 5 1/2 x 11 1/2 | 140 x 292 |
North American Standard 8-by Timber (Surfaced 4 Sides, S4S)
| NOMINAL SIZE (INCHES) | ACTUAL SIZE (INCHES) | ACTUAL SIZE (MM) |
|---|---|---|
| 8 x 8 | 7 1/2 x 7 1/2 | 191 x 191 |
| 8 x 10 | 7 1/2 x 9 1/2 | 191 x 241 |
| 8 x 12 | 7 1/2 x 11 1/2 | 191 x 292 |
Softwood Lumber Lengths
Softwood lumber comes in a number of standard lengths as listed in the table below. According to NIST Publication P20, actual lengths must be at least equal to the nominal length, but can be up to 3" longer than the nominal length.
| LENGTH IN FEET | LENGTH IN INCHES | LENGTH IN METERS |
|---|---|---|
| 6 feet | 72 inches | 1.829 meters |
| 8 feet | 96 inches | 2.438 meters |
| 10 feet | 120 inches | 3.048 meters |
| 12 feet | 144 inches | 3.658 meters |
| 14 feet | 168 inches | 4.267 meters |
| 16 feet | 192 inches | 4.877 meters |
| 18 feet | 216 inches | 5.486 meters |
| 20 feet | 240 inches | 6.096 meters |
| 22 feet | 264 inches | 6.706 meters |
| 24 feet | 288 inches | 7.315 meters |
Hardwood Lumber Dimensions
Hardwood lumber is sized based on how many sides are surfaced. Surfaced refers to a finishing process that smooths the lumber to remove all saw marks.
In North America, hardwood lumber is usually specified using the quarter system, where a board is identified by its thickness in quarters of an inch. For instance, hardwood trim that ends up being just over 1" thick (surfaced on 2 sides) is called a five-quarter (5/4) board.
Hardwood board widths vary. In most cases, hardwood boards come in random widths to be ripped to size by the woodworker. However, in some cases, like the big-box hardware stores, the boards come in dimensional widths similar to softwood widths. It is advisable to check with your contractor or lumber supplier before finalizing design details so you aren't surprised by what you receive.
| NOMINAL SIZE | ROUGH SIZE | ACTUAL SIZE: SURFACED 1 SIDE | ACTUAL SIZE: SURFACED 2 SIDES |
|---|---|---|---|
| – | 1/2 inch | 3/8 inch (9.5 mm) | 5/16 inch (7.9 mm) |
| – | 5/8 inch | 1/2 inch (13 mm) | 7/16 inch (11 mm) |
| – | 3/4 inch | 5/8 inch (16 mm) | 9/16 inch (14 mm) |
| 4/4 inch | 1 inch | 7/8 inch (22 mm) | 13/16 inch (21 mm) |
| 5/4 inch | 1 1/4 inch | 1 1/8 inch (29 mm) | 1 1/16 inch (27 mm) |
| 6/4 inch | 1 1/2 inch | 1 3/8 inch (35 mm) | 1 5/16 inch (33 mm) |
| 8/4 inch | 2 inches | 1 13/16 inch (46 mm) | 1 3/4 inch (44 mm) |
| 12/4 inch | 3 inches | 2 13/16 inch (71 mm) | 2 3/4 inch (70 mm) |
| 16/4 inch | 4 inches | 3 13/16 inch (97 mm) | 3 3/4 inch (95 mm) |
Glue Laminated Lumber Dimensions
The following table comes from the American Institute of Timber Construction's Standard Specification for Structural Glued Laminated Timber of Hardwood Species publication.
ANSI/AITC A190.1-1992 allows for any width and depth of glue laminated timber. Standard widths are specified in the above publication, but can be customized as needed. A wide range of depths are available, far too many to list here, so please contact your local manufacturer for more information on their offerings - in general depths start at 6" and go up to 30" and beyond. Of course, lengths are customized for each job.
| NOMINAL WIDTH | ACTUAL FINISHED WIDTH |
|---|---|
| 3" | 2 1/2" |
| 4" | 3 1/8" or 3 1/2" |
| 6" | 5 1/8" or 5 1/2" |
| 8" | 6 3/4" |
| 10" | 8 3/4" |
| 12" | 10 3/4" |
| 14" | 12 1/4" |
| 16" | 14 1/4" |
