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What Does 4/4 Mean When Talking About Lumber?

by Mark Stephens | August 9th, 2013

Hardwood lumber comes in thicknesses measured in quarters of an inch. 1″ lumber is called 4/4 (four quarters). 2″ lumber is called 8/4 (eight quarters). Here’s how they compare.

Pardon me, but what does 4/4 mean?

Chances are the first time you stepped foot into a hardwood lumber dealer you saw all these crazy fractions flying at you: 4/4, 5/4, 6/4, 8/4 and so on.

They’re industry terms that not everyone knows, but they refer to the thickness of the lumber. Hardwood lumber thickness is communicated in quarters of an inch.

rough hardwood lumber board

With rough lumber, it’s hard to see the grain and the boards are frequently slightly cupped or warped from the drying process. Surfacing fixes both of these, but it does remove thickness.

Let’s start with the most common: 4/4.  If we were talking you’d hear me say it as “four quarters,” which is short for four quarters of an inch.  If you’re pretty snappy with numbers, you’ve already put together that 4/4 is equal to one inch.

4/4 = 1″ thick
5/4 = 1-1/4″ thick
6/4 = 1-1/2″ thick
8/4 = 2″ thick
12/4 = 3″ thick

There’s another designation that might confuse you: S2S.  That means “surfaced two sides.” A saw that cuts lumber from a log is very large and aggressive, so the resulting lumber is known as “rough sawn” and the surfaces of the boards are . . . yes, rough.

Enter S2S. Lumber that is S2S has been planed smooth and flat. Naturally, that process removes some thickness and answers the age old question, “Why isn’t 4/4 lumber a full one inch thick?”

Actual measured thickness on 4/4 lumber that’s S2S is 13/16″.  Make sense?

Rough lumber needs to be dressed with a planer and/or jointer and this is where a lumber dealer like ourselves has to make a tough decision. Have the lumber surfaced smooth and clean, or sell it rough? There are benefits to both, but it’s impractical to stock both. Rough lumber costs less, and the woodworker is often able to yield thicker boards. Surfaced lumber, on the other hand, is much easier to see the grain and color when selecting boards, and the woodworker doesn’t necessarily need a planer in order to work with the material, making it easier on the less experienced woodworkers out there.

We’ve decided to stock surfaced lumber.

Here are pictures of each lumber thickness to help you out (left column shows each with a ruler, the right column without):

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This entry was posted on Friday, August 9th, 2013 at 11:54 am and is filed under Tips and Tricks. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.

11 Responses to “What Does 4/4 Mean When Talking About Lumber?”

  1. Mike in Wickenburg says:

    Great info for the beginner.

    But, I do have a question: When repairing or re-tightening wooden chairs, it is necessary to sand the inside of the dowel holes to remove old glue. In the past, I have made my own sanding sticks by wrapping sandpaper around a 1/2 dowel. Is the a product readily available that I can use instead?

    • Sure, you can use a drill bit the same size as the hole. You just need to do a little reaming. With a power drill you risk enlarging the hole, which you don’t want to do. Just use a drill bit in a pair of vise grips and gently ream out the hole. Faster and arguably better than sanding.

  2. juegos en hospitales says:

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  3. SR says:

    so I guess the answer is a resounding “no” that I can’t ask Mark a question about his post on Sapwood in Walnut from March. Thanks!

    • Sure you can! Please post it again if it’s gone unanswered. Sadly, there’s an obscene amount of spam that gets run through the comments every day and so they have to be checked over manually for the “real” ones. Perhaps yours got overlooked, if that’s the case please accept my apologies. It’s not intentional. Re-post it, email me (mark@woodworkerssource.com) or call 480-344-1020 xt 110. I’m happy to help.

  4. Raiders says:

    This is very cool. Thanks for the info. Now, is 1/2″ lumber common-
    that is, is it sold at most lumer yards?

    • No, not exactly common. Anything thinner than 1″ is actually planed down from thicker lumber, rather than sawn from a log with the intention of becoming 1/2 or 3/8 or whathaveyou. “Thin” stock is a convenience item.

  5. Zak says:

    Thank you this was well written and explained. I found it informative and helpful, thank you for posting it.

  6. Tg says:

    Very helpful! Thanks

  7. matt says:

    what about a composite material

  8. Try to find white oak.