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Actual vs. Nominal Lumber Dimensions: What’s the Difference? 

A board with a 1 x 4” nominal size and a ¾ x 3.5” nominal size with both measurements shown. 

Ok. You have your project plans ready to go and are taking the next big step – buying the dimensional lumber. But then, confusion sets in when you realize the product you’re looking for has two different names. Oh no!

It’s important to know that when it comes to the size of finish grade lumber, there’s a difference between what the board is called (its nominal size) and its actual size.

This, of course, can be a little confusing for beginner DIY woodworking enthusiasts – but it doesn’t have to be. Let’s take a look at the difference so you can get accurate and precise results whenever you’re working with dimensional lumber.

Nominal vs. Actual Dimensional Lumber Sizes Explained

Nominal lumber sizes like 1 x 4 and 1 x 6 make you think that the width and thickness of the lumber are 1 inch and 4 inches or 1 inch and 6 inches. However, this isn’t actually the case.

In reality, nominal dimensions refer to the size of the lumber before it undergoes drying, planing and surfacing at the lumber yard. The finished size (aka the actual size) is different from the common (nominal) name. This means that the nominal measurements are larger than the actual measurements of each board, and that difference varies based on the piece of lumber you’re buying.

When it comes to lumber from Baird Brothers, all of our 1 inch products (like 1 x 4 or 1 x 6) are ACTUALLY ¾ inch (¼ under the first number) and half an inch under the second number. This means a 1 x 4’s actual dimensions are ¾ x 3 ½ inches and a 1 x 6 is actually ¾ x 5 ½.

The actual dimensions of our 2 inch products are (in most cases) half an inch under both nominal numbers (ex. 2 x 8 is actually 1 ½ inches by 7 ½ inches). The outlier is our 2 x 2 product. No matter the species ordered, 2 x 2 from Baird Brothers is always 1 ¾ x 1 ¾ (a ¼ inch under each nominal number).

5/4 products (like 5/4 x 6 lumber) also have finished dimensions that are different from the common (nominal) name. After drying and sanding, the 5/4 inch size is reduced to a 1 inch net. Then, the second number is reduced by a half an inch. So, in the end, lumber that is called 5/4 x 6 is actually 1 inch by 5 ½ inches.

Quick Comparison of Standard Lumber Measurements

1” Dimensional Lumber Examples

Nominal Size: 1 x 2 Actual Size: ¾ x 1 ½

Nominal Size: 1 x 3 Actual Size: ¾ x 2 ½

Nominal Size: 1 x 4 Actual Size: ¾ x 3 ½

Nominal Size: 1 x 6 Actual Size: ¾ x 5 ½

Nominal Size: 1 x 8 Actual Size: ¾ x 7 ½ 

Nominal Size: 1 x 10 Actual Size: ¾ x 9 ½ 

Nominal Size: 1 x 12 Actual Size: ¾ x 11 ½ 

2” Dimensional Lumber Examples

Nominal Size: 2 x 2 Actual Size: 1 ¾ x 1 ¾ (outlier)

Nominal Size: 2 x 4 Actual Size: 1 ½ x 3 ½ 

Nominal Size: 2 x 6 Actual Size: 1 ½ x 5 ½ 

Nominal Size: 2 x 8 Actual Size: 1 ½ x 7 ½

Nominal Size: 2 x 10 Actual Size: 1 ½ x 9 ½

Nominal Size: 2 x 12 Actual Size: 1 ½ x 11 ½

5/4” Dimensional Lumber Examples

Nominal Size: 5/4 x 4 Actual Size: 1 x 3 ½ 

Nominal Size: 5/4 x 6 Actual Size: 1 x 5 ½

Nominal Size: 5/4 x 8 Actual Size: 1 x 7 ½ 

Nominal Size: 5/4 x 10 Actual Size: 1 x 9 ½ 

Nominal Size: 5/4 x 12 Actual Size: 1 x 11 ½  

Breaking Down Actual Lumber Sizes

Still not sure? Our very own Ben Baird can help you out. Listen as he explains the difference between nominal and actual lumber dimensions for various board sizes.

Always Be Mindful of What Affects Natural Materials

Moisture content, shrinkage, and surfacing techniques all impact the final size of a piece of lumber. Hardwood lumber, softwood lumber, pressure-treated lumber: you’ll see the two types of sizes everywhere you turn.

When you’re on the hunt for hardwood products, be mindful of the fact that the drying process can sometimes result in defects. If you’re not sourcing lumber from a manufacturer that uses the latest technology (like our Woodeye scanner), then you need to keep an eye out for certain issues: warping, cracks, cupping and grain separation.

It’s also important to remember that no matter what type of DIY project you’re working on, when it involves dimensional lumber, mouldings or hardwood flooring, you need to let the lumber breathe and adjust to its new environment before you begin cutting.

Finding the Right Hardwood Lumber

When it comes to understanding actual vs. nominal lumber dimensions, you can navigate buying lumber for your next woodworking project without fear. Many companies go the extra mile nowadays to list both the nominal size and the actual size.

And for customers who still need some extra support or product suggestions, that’s where our customer service team members come in! They’re ready to walk through your project details and make the suggestions you’re looking for!

So, now that you understand the sizes, pick out that lumber and start making some sawdust!

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