Do you feel like actual size of 2×8 is smaller than what it claims on the label? Due to processing, the actual size becomes smaller. For example, softwood loses around half an inch after processing.
Dimensions displayed commercially are called nominal size. If you’re unfamiliar with these measurements, scroll down and I will explain how it works and why the actual size is smaller!
Actual Dimensions of a 2×8 Board
Advertised 2×8 board actually has a dimension of 1 ½ ″ by 7 ¼ ″. 2×8 is its nominal size — lumber’s original size before undergoing necessary processes.
The actual size is slightly smaller than its nominal size, and it is to be expected. The size of lumber sellers displayed in stores and commercials is based on measurements after lumber is cut into shapes.
Actual Measurements of Dimensional Lumber
If you measure the lumber’s dimension being sold, you’ll notice it is slightly smaller than its nominal size displayed commercially. This is established in woodworking. For example, actual size of 2×8 board has a difference of at least half an inch.
The actual size becomes smaller because it dries due to processing. Another reason is that distributors smoothen the surface of lumber with planers before they sell it. Blade sizes are also a factor because some wood parts are converted to sawdust during the cutting process.
However, modern technologies used in cutting and planing lumber are more precise, resulting in lesser reduction of actual size from its original size. The good thing is it only applies to cross sections of wood (height x width), and actual length remains exactly what you ask for.
Basic Lumber Sizing
Cross section (height and width of lumber) is the basic sizing displayed in stores. And unlike width and height, length depends on how much you need. So if you buy five feet of 2×8 board, you’ll receive wood with an actual size of 1 ½ ″ x 7 ¼ ″ x 5 ″.
Dimension is vital to know the right size for buildings or residential homes. Basic lumber sizing is consistent for everyone in the country, whether you do DIY, professional carpenter, or doing household repairs.
Having standard sizes helps you decide which size works best on your beams, walls, or frames for your floor. Is 2×6 too much for my rafters? Or if you probably need bigger beams on larger houses and so on.
Dimensional Lumber vs. Nominal Dimensions: Why is it Smaller?
As mentioned, actual dimension of lumber is smaller than nominal dimensions because it undergoes processing. The dimensions you see in stores are nominal dimensions to avoid confusion.
To know how to get the actual dimension of softwoods, subtract half an inch for nominal sizes above 2. If your nominal size is 3″, then its actual size would be 2 ½″.
Nominal sizes below 2 ″ reduces ¼ ″, so 1 ″ becomes ¾ ″. And on nominal sizes 8 and above, you reduce ¾ ″ to get the actual size. For example, the actual size of 4×10 is 3 ½ ″ x 9 ¼ ″.
Nominal Size
Nominal size is the label of wood dimensions in stores. It is based on initial wood measurement before it is cut and processed into varieties and sizes.
Nominal dimensions use whole numbers, while actual sizes may have fractions that can be overwhelming to the eyes and takes longer time to say. That is why it makes more sense for dealers to display nominal dimensions.
Actual Size
Actual size of wood is the true measurement of wood after it’s been cut and processed for distribution. For example, actual size of 2×2 is 1 ½ ″ x 1 ½ ″, or 38mm x 38mm.
1x Board
This lumber grade has actual thickness of less than an inch. This can be called cabinet grade or no. 1 grade because it is meant for small constructions like cabinets and furniture frames.
2x Board
No. 2 grades or 2-by wood is a lumber grade with less than 2 inches of thickness. This is designated as standard grade commonly used for framing houses and general constructions.
2×6 wood can even support foundations, while 2×8 and wider are ideal for decks and multi-story buildings.
When Do Nominal and Actual Sizes Match?
Lumber sold nowadays follows standard lumber sizing, where nominal size is always bigger than actual size. Distributors value quality of their products. That’s why they always process their wood before selling it, resulting in size reduction.
But there are instances sizes on old lumber from old constructions match. This is because standardization was different before.
So if you measure old beams on your ancestral house and their nominal size matches the actual size, that’s because both sizes used to match.
2×8 Size of Different Materials
In some cases, difference between nominal and actual sizes is inconsistent and doesn’t follow the formula explained above. Different breeds of hardwoods and softwoods affect it.
However, actual measurements on softwoods are consistent. Hardwoods and glue laminated lumber have different actual sizes since they are sold in board dimensions instead of by length.
Plywood and Other Sheets
Plywood sizes comes in 2×2 ft, 2×2 ft, 4×4 ft, with 4×8ft being the most common. Utility plywood can even measure up to 5 to 10 ft. Actual thickness of unsanded plywood is the same as nominal size. But it loses 1/32 in when sanded.
On 1 ¼ and 1 ⅛ plywood, difference is unnoticed. However, actual size of ¾ plywood becomes 23/32, ½ becomes 15/32, and so on.
Hardwood Lumber Length
Actual size of hardwood’s cross-section varies on how many sides of it are surfaced. But its length is constant. Standard lengths available in the US and Canada in feet are 6, 8, 10, 12, 14, 16, 20, 22, and 24.
Hardwood Lumber Dimension
Sizing hardwood uses quarter system. When you see its sizes in stores displayed as 4/4, that means it is 1 inch thick. Each number represents a quarter inch, hence its name. So a 5/4 nominal size means it is 1 ¼″ thick, 8/4 is 2″, 6/4 is 1 ½ ″, you get the idea. Know more about the 5/4 lumber here!
Hardwood is surfaced on one side or two sides, and it can affect its actual size. One side reduces ¼ of an inch, so nominal thickness of 1″ has an actual size of ⅞ when only a side is surfaced and 13/16″ when surfaced twice.
| Nominal Thickness in Inches | Surfaced 1 Side in Inches | Surfaced 2 side in Inches |
| 1/2 | 3/8 | 5/16 |
| 3/4 | 5/8 | 9/16 |
| 17/8 | 7/8 | 13/16 |
| 1 1/4 | 1 1/8 | 1 1/16 |
| 1 1/2 | 1 3/8 | 1 5/16 |
| 2 | 1 13/16 | 1 /34 |
| 3 | 2 13/16 | 2 3/4 |
| 4 | 3 13/16 | 3 3/4 |
Glue-Laminated Dimensions
The table below follows the Standard Specification for Structural Glued Laminated Timber of Hardwood Species published by American Institute of Timber Construction.
Nominal width starts in 3 inches, and sizes are sold in different dimensions and can be customized.
| Nominal Width in Inches | Actual Width in Inches |
| 3 | 2 1/2 |
| 4 | 3 1/2 |
| 6 | 5 1/2 |
| 8 | 6 3/4 |
| 10 | 8 3/4 |
| 12 | 10 3/4 |
| 14 | 12 1/4 |
| 16 | 14 1/4 |
Softwood Lumber Length
The actual and nominal length on softwood remain the same even after processing. When you buy 10 feet of 4×6, actual size of cross-section will change to 3 ½ ″ x 5 ½ ″, while length will have no obvious change and still remains 10 feet.
Softwood Lumber Dimension
The National Institute of Standards American Softwood Lumber Standard (PS 20) standardized softwood lumber dimensions [1]. So you can use the formula explained earlier to determine the actual size from its nominal size.
FAQ
What are the symbols for inches and feet?
The symbols for inches and feet are denoted by double prime (″) after a number to indicate inches and single prime (′) for feet. Remember that double (“) and single quotation marks (‘) used in writing direct speech are different but are often confused with primes.
If you write 5 feet and 9 inches using these symbols, it will look like this, 5′ 9″. Feet and inches can also be abbreviated into ft and in, respectively. Either way, both are correct.
These symbols are widely recognized and used in various fields, such as construction, engineering, and everyday measurements, to indicate specific lengths in the imperial system.
What is the actual size of a 2×6 lumber?
The actual size of a 2×6 lumber is 1½ in by 5½ in, or 38mm by 140mm in metric system. As advertised, 2×6 lumber is only the nominal size, which is the original dimension of lumber before it undergoes processing. And as you noticed, sizes slightly shrank afterward.
Conclusion
So, to get the actual size of 2×8, subtract 2 by ½ and 8 by ¾, and you’ll get 1 ½ ″ x 7 ¼ ″ of wood’s actual size. This formula consistently works on softwood. However, determining the sizes of hardwood and glue-laminated wood can be a bit confusing.
Nonetheless, expect that actual measurement will be a few inches smaller than what it claims on the label.
You've probably seen his down-to-earth wisdom in USA Today, Bobvila, Family Handyman, and The Spruce, where he has shared commentary and guidance on various woodworking topics.
Robert is the brain behind Sawinery, where he aims to share tips, tricks, and a passion for all things carpentry.
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