What’s the Reason for Nominal Dimensions?

For many of us, the moment we learned that a 2×4 board is actually 1.5 inches x 3.5 inches was simply mind-blowing.

For many of us, the moment we learned that a 2×4 board is actually 1.5 inches x 3.5 inches was simply mind-blowing. The reason for this apparent contradiction is that the board has been planed down to eliminate irregularities. At one point, many years ago, 2x4s actually were 2 inches x 4 inches, but their rough surfaces made them difficult to stock and handle. The old terms, such as 2×4 or 4×4, are still used, and are known as the “nominal” size of the board. These nominal sizes are used because they are easier to say and they stick to tradition. Now, thanks to a lawsuit, most big box stores list the nominal and actual sizes of lumber.

If you need help keeping the different sizes of nominal vs. actual lumber sizes straight, use the charts included in our article, Making Sense of Lumber Sizes.

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