Dimensional Lumber: Nominal vs Actual

{Did You Know?}

A 2×4 is actually NOT 2 inches by 4 inches?!? This is one of those tips that I have learned the hard way!

Dimensional lumber is measured by a “Nominal Dimension” or it’s common name (ie 2×4) which is the dimension prior to being milled down. Dimensional Lumber is also measured by an “Actual Dimension” which is the actual size of the piece of lumber after it is milled and plained (ie 1-1/2” x 3-1/2”).

When measuring a new project you ALWAYS want to use the actual dimensions. Trust me, every 1/2” and 1/4” difference can add up and make your final dimensions very skewed.

This recently happened to me. I wanted to use 1×8 boards to create a table top and match the existing dimension of 30” wide. I, without looking, assumed (you know what they say about that) that the actual width would be 7-1/2”. This would perfectly add up to my desired 30”.


The actual dimension for a 1×8 is actually 3/4” x 7-1/4”. I was going to be a full inch off. Normally that inch may have been “ok” but I needed this project to be precise. I am so grateful that I double and triple checked my math which saved my time and money.

I created this easy to use chart to help you know the difference between common Nominal and Actual Dimensions.

Save this chart for future projects!

If you are ready for your first project using dimensional lumber check out my easy beginner friendly DIY tutorials for a Simple Wood Frame, Floating Shelves, Modern Barn Door, and my favorite Board and Batten accent wall.

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