Lumber Dimensions | Nominal vs. Actual Sizes

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A huge part of being a skilled woodworker is a deep understanding of lumber dimensions, allowing you to cut the right length, width, and thickness. However, determining the difference between nominal and actual sizes isn’t the easiest skill to master. 

If you’re having difficulty understanding these metrics, here’s a short explanation from our resident woodworkers to ease your worries. 

What is Dimensional Lumber?

Newbie woodworkers may get confused with what dimensional lumber means, but it’s simply referring to a wood material cut into a standard size range. It means that these materials have pre-determined length, width, and depth when sold in the market. 

milling spruce log to lumber

This term is used when referring to softwood boards and pieces like pines. You’ll also hear it more often when trading materials for framing and carpentry. 

If you’re familiar with the wood market, you’ll know that these common wood products come in 4×4 and 2×4 dimensions. However, you can’t expect a 2×4 dimensional lumber to have 2 by 4 actual dimensions. Read along as we explain these sizing metrics thoroughly.

Nominal vs. Actual Sizes

You may not know, but the nominal dimensions the lumber has been labeled with aren’t exactly its actual size. It’s typically larger than the real size range because it’s the plywood dimensions taken before the material went under drying, surfacing, and sanding. 

milling lumber

Now, why is a 2×4 not 2×4 in actual sizing? It’s because the actual measurement of 2×4 turns 1 1/2 x 3 1/2 inches or 38 x 89 mm after processing the material. 

If you’re buying green southern pine lumber, the drying process will likely shrink its 2×4 actual measurement into an even smaller dimension. 

The same goes for other softwood boards in different sizes, as the actual size of 1×6 is 3/4 x 5 1/2 inches or 19 x 140 mm. Fortunately, modern technologies allow minimal shrinkage and material removal to maintain the original dimensions of a board with 2×4 or 1×6 actual size.  

Nominal Size RangeActual Size Range
1×2 inches3/4 x 1 1/2 inches
1×3 inches3/4 x 2 1/2 inches
1×4 inches3/4 x 3 1/2 inches
1×5 inches3/4 x 4 1/2 inches
1×6 inches3/4 x 5 1/2 inches
1×8 inches3/4 x 7 1/4 inches
1×10 inches3/4 x 9 1/4 inches
1×12 inches3/4 x 11 1/4 inches
2×2 inches1 1/2 x 1 1/2 inches
2×3 inches1 1/2 x 2 1/2 inches
2×4 inches1 1/2 x 3 1/2 inches
2×6 inches1 1/2 x 5 1/2 inches
2×8 inches1 1/2 x 7 1/4 inches
2×10 inches1 1/2 x 9 1/4 inches
2×12 inches1 1/2 x 11 1/4 inches
4×4 inches3 1/2 x 3 1/2 inches
4×6 inches3 1/2 x 5 1/2 inches
6×6 inches5 1/2 x 5 1/2 inches

Hardwood Lumber Measurements

Instead of measuring 2×4 actual dimensions in terms of width and length, measuring hardwood boards are often associated with their nominal thickness. These wood types include stock from oak, mahogany [1], and maple trees that are not sold in standard sizes. 

When buying hardwood boards near you, it doesn’t include the problem of determining the actual dimensions of a 2×4 material because its sizing indicates if the stock is surfaced on one or two sides. 

CCA-Treated Lumber wood

These materials are not commonly sold in 4×4 or 2×4 dimensions because they’re marketed by the board foot. 

In simpler terms, one board foot is equivalent to 144 cubic inches of the wood board. It means that the wood’s thickness is 1 inch with a width of 12 inches. 

However, just because you don’t need to find a 2×4 doesn’t mean choosing hardwood lumber is bliss. These materials are sold in quarters, where one unit refers to ¼ inch depth.  

Read Next: Feet and Inches Symbols in Woodworking 

Nominal ThicknessS1S (Surfaced on one side)S2S (Surfaced on two sides)
½ inches3/8 inch or 9.5 mm5/16 inch or 7.9 mm
⅝ inches1/2 inch or 13 mm7/16 inch or 11 mm
¾ inches5/8 inch or 16 mm9/16 inch or 14 mm
1 or 4/4 inches7/8 inch or 22 mm13/16 inch or 21 mm
1 ¼ or 5/4 inches1 1/8 inches or 29 mm1 1/6 inches or 27 mm
1 ½ or 6/4 inches1 3/8 inches or 35 mm1 5/16 inches or 33 mm
2 or 8/4 inches1 13/16 inches or 46 mm1 3/4 inches or 44 mm
3  or 12/4 inches2 13/16 inches or 71 mm2 3/4 inches or 70 mm
4 16/4 inches3 13/16 inches or 97 mm3 3/4 inches or 95mm

How About Plywood?

When you shop for plywood materials, the most common size range you’ll encounter is around 4 feet by 8 feet. The nominal thickness for these wooden boards also varies between two options: ½ inch and ¾ inch. 

buying plywood

However, remember that the actual sizes for these materials are reduced after processing. You’ll also find the plywood labeled with different quality grades from A to D on each side to determine their surface smoothness. 

FAQ

Is 2x6 stronger than 2x4?

Yes, 2×6 is stronger than 2×4. The actual size of 2×4 is only one and a half inches thick and 3 1/2 inches wide, while 2×6 boards have 1 1/2  inch thickness and 5 1/2 inches width.

Is it cheaper to build with 2x4 or 2x6?

It is cheaper to build with 2×4 lumber because 2×6 has an actual dimension two inches wider than it. Besides, 2×4 materials have a 4-inch depth difference from 2×6. 

Conclusion

When you become well-versed in lumber dimensions, buying the right material for your next project won’t be as complicated as you think. 

After all, these woodworking basics will be your foundation in building a better craft in the future. Trust our wood experts when we say it will also help you spend less money on the wrong material. 

Robert Johnson is a woodworker who takes joy in sharing his passion for creating to the rest of the world. His brainchild, Sawinery, allowed him to do so as well as connect with other craftsmen. He has since built an enviable workshop for himself and an equally impressive online accomplishment: an extensive resource site serving old timers and novices alike.
Robert Johnson
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