SIP Panels and Dimensional Lumber Sizes: Nominal vs. Actual

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 sizes so many common North American lumber sizes. The reason it is important to know this information is that you want to be sure your SIP Panels and the dimensional lumber you use are the same. This is especially true if you are inserting lumber between the skins of the SIP Panel.

Available Tables

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 20-10).

North American Standard 1-by Lumber

Nominal Size (inches)Actual Size (inches)Actual Size (mm)
1 x 23/4 x 1 1/219 x 38
1 x 33/4 x 2 1/219 x 64
1 x 43/4 x 3 1/219 x 89
1 x 63/4 x 5 1/219 x 140
1 x 83/4 x 7 1/419 x 184
1 x 103/4 x 9 1/419 x 235
1 x 123/4 x 11 1/419 x 286

North American Standard 2-by Lumber

Nominal Size (inches)Actual Size (inches)Actual Size (mm)
2 x 21 1/2 x 1 1/238 x 38
2 x 31 1/2 x 2 1/238 x 64
2 x 41 1/2 x 3 1/238 x 89
2 x 61 1/2 x 5 1/238 x 140
2 x 81 1/2 x 7 1/438 x 184
2 x 101 1/2 x 9 1/438 x 235
2 x 121 1/2 x 11 1/438 x 286

North American Standard 3-by Lumber

Nominal Size (inches)Actual Size (inches)Actual Size (mm)
3 x 32 1/2 x 2 1/264 x 64
3 x 42 1/2 x 3 1/264 x 89
3 x 62 1/2 x 5 1/264 x 140
3 x 82 1/2 x 7 1/464 x 184
3 x 102 1/2 x 9 1/464 x 235
3 x 122 1/2 x 11 1/464 x 286

North American Standard 4-by Lumber

Nominal Size (inches)Actual Size (inches)Actual Size (mm)
4 x 43 1/2 x 3 1/289 x 89
4 x 63 1/2 x 5 1/289 x 140
4 x 83 1/2 x 7 1/489 x 184
4 x 103 1/2 x 9 1/489 x 235
4 x 123 1/2 x 11 1/489 x 286

North American Standard 6-by Lumber

Nominal Size (inches)Actual Size (inches)Actual Size (mm)
6 x 65 1/2 x 5 1/2140 x 140

North American Standard 8-by Lumber

Nominal Size (inches)Actual Size (inches)Actual Size (mm)
8 x 87 1/4 x 7 1/4184 x 184

Softwood Lumber Lengths

Softwood lumber comes in a number of standard lengths as listed in the table below.

Length in FeetLength in InchesLength in Meters
6 feet72 inches1.829 meters
8 feet96 inches2.438 meters
10 feet120 inches3.048 meters
12 feet144 inches3.658 meters
14 feet168 inches4.267 meters
16 feet192 inches4.877 meters
18 feet216 inches5.486 meters
20 feet240 inches6.096 meters
22 feet264 inches6.706 meters
24 feet288 inches7.315 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 SizeRough SizeActual Size: Surfaced 1 SideActual Size: Surfaced 2 Sides
1/2 inch3/8 inch (9.5 mm)5/16 inch (7.9 mm)
5/8 inch1/2 inch (13 mm)7/16 inch (11 mm)
3/4 inch5/8 inch (16 mm)9/16 inch (14 mm)
4/4 inch1 inch7/8 inch (22 mm)13/16 inch (21 mm)
5/4 inch1 1/4 inch1 1/8 inch (29 mm)1 1/16 inch (27 mm)
6/4 inch1 1/2 inch1 3/8 inch (35 mm)1 5/16 inch (33 mm)
8/4 inch2 inches1 13/16 inch (46 mm)1 3/4 inch (44 mm)
12/4 inch3 inches2 13/16 inch (71 mm)2 3/4 inch (70 mm)
16/4 inch4 inches3 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 to 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 WidthActual 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″