Nominal Vs. Actual Dimensions Of Lumber

You’re looking to pick up some lumber for your next project. Whether you’re designing furniture, building a structure, or framing a wall, you need the measurements to be exact.

You pick up the quantity of lumber you need, but when you get home and measure it, you find that the numbers don’t match what you saw at the store.

What? How could one piece of wood have two different measurements?

It’s due to something called nominal measurements and actual dimensions; two different systems used to size lumber.

What Is a Nominal Measurement?

Nominal sizes are the terms you often hear to describe lumber, like a 2 x 4 or 4 x 4. They’re a general category that lumber falls within, but do not reflect the actual sizes after the wood is dried and planed. Basically, a nominal measurement describes the dimensions of the wood before it’s finished.

The nominal dimensions are slightly larger than the actual measurements due to the drying and planning process. 

What Does Actual Size Refer to?

When you buy wood at a store, you’ll see its nominal measurements listed. But once the wood is dried and surfaced, it will match the actual or minimum dressed measurements. During this process, the width shrinks on all four sides, so the actual sizes are always slightly smaller than the nominal sizes. 

Common Nominal & Actual (or Minimum) Measurements

Now that you understand the differences between these two sizing systems, it’s time to apply what you’ve learned to the measurements you’ll find in a store. 

But there’s another factor to consider here: Whether you’re buying softwood lumber, hardwood, or plywood.

Softwood lumber

Often used for construction or framing purposes, softwood lumber is utilized a lot. A few popular species include pine or fir.

As we mentioned earlier, the nominal size of dimensional lumber is greater than the actual measurements. When the wood is first cut, it will match the nominal size (for example, 2 x 4), but once it’s planed and dried, it shrinks to 1 ½ x 3 ½.

Here’s a handy table for reference: (Source: Measurite)

Hardwood

Next up is hardwood; popular species include maple, oak, and birch. These types of wood are more commonly used to make furniture. Like softwood, there’s a difference between the nominal and actual lumber sizes. 

And there’s yet another factor to consider when you’re selecting the size: Has the wood been surfaced on one side (SIS) or two sides (S2S)?
On top of that, hardwood lumber isn’t sold in the same dimensions as softwood lumber. It’s sold by the board foot; each board foot is 1” thick, 1” long, and 12” wide. 

Here’s a look at the different sizes available for hardwoods: (Source: TheSpruceCrafts)

Plywood

You can purchase this type of lumber in sheets, typically sized 4’ x 8’. Again, the actual size of your plywood sheet will be slightly less than the nominal dimensions. 

Shop Our Selection of Lumber

Still not sure which size (or type) of lumber you need? At STAR Building Materials, we carry lumber in Winnipeg. On our website, you’ll find spruce, cedar, wagon oak, and more. We list the nominal thickness and width of our lumber on each product we carry. 

We can help you select the right dimensions and quantity for your next project. Contact us today!