What Are Standard Lumber Sizes for Woodworking

What are standard lumber sizes? Lumber sizes vary based on a number of key factors. If you're planning to purchase lumber for an important woodworking project, you'll need to know how to find the right size for your needs.

What's the Real Measurement?
When you see a lumber size like 2 x 4, some people think you're getting lumber that's 2 inches thick by 4 inches wide. Depending on the wood you're buying, that may not actually be the case. Most of the wood you buy is actually dressed wood, or finished wood, which has gone through a planer to smooth it down. Dressed wood may vary by as much as half an inch, so a piece of dressed 2 x 4 is actually closer to 1 1/2 x 3 1/2 inches. Kiln-dried wood will be a little smaller than this.

Know the Terms
When you're looking for lumber, you need to know whether you're looking for rough wood or dressed wood. There are a couple of different ways to designate dressed wood. For wood that's dressed on all four sides, you might look for S4S. For wood dressed only on two sides, you should look for S2S. Dressed wood typically varies by a half inch from the nominal size.

Nominal size refers to the initial lumber size, or the size that the lumber company uses. For example, wood that's 2 inches by 4 inches would have a nominal size of 2 x4. After dressing, that piece of wood will still be called a 2 x 4, but the dimensions are half an inch smaller.

Softwood actual sizes vary from the nominal size, depending on whether the wood is dried or green. Dried wood sizes typically vary anywhere from a quarter of an inch to a half inch from the nominal size. When wood dries, it shrinks, so it's smaller than the nominal size. Green wood sizes may vary, but green wood is not dried, and you should take into account that it's going to shrink when it dries.

Hardwood Sizes
Hardwood is typically labeled as a derivation of four, based on quarter-inch thicknesses. Therefore, a half-inch thick piece of hardwood would be 2/4. The system of fours extends beyond the inch mark, too; a piece of wood that's two inches thick would be labeled as 8/4.

Because hardwood is scarcer than softwood, the measurements of hardwood may not be quite as standard. The dimensional lumber size of hardwood may vary based on the hardwood itself; it may be narrower or wider than the nominal size, depending on the lumber. Because of its relative scarcity, hardwood isn't scrapped just because it doesn't conform with the standard size, and people who use hardwood must understand that the actual size may vary from the nominal size.

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