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Woodworking 101: What Does 4/4 Mean In Lumber?

by Mark Stephens | April 28th, 2014

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.

What do these lumber fractions mean? 4/4, 5/4, 6/4, 8/4, 10/4, 12/4

In short, these fractions refer to the thickness of hardwood lumber. The thickness is read in increments of quarters of an inch.

Why those funny fractions? I’m used to standard sizes like 1×6, 1×12, 2×8 etc.

While you might be used to seeing sizes like 1×6 or 2×8 in lumberyards for softwoods like fir, pine and cedar, the hardwood industry takes a different approach. The softwood industry is vastly different from the hardwood industry. That’s because the primary users of hardwoods (such as red oak and cherry, for example) build custom or made-to-fit products – like furniture and cabinetry – where uniform sizes in the raw material is unnecessary. For example, there’s no standard size for kitchen tables, you can make one any size you want. So sawmills cut hardwood logs to get the best yield from a log, which means all boards will be various in width rather than the same width. If they were cut for specific sizes or uniform widths, there would be more waste, more time, and therefore the resulting boards would cost you more money. Softwoods that get sold in “standard” sizes like 1×6 and 2×8 are cut for particular applications that require those sizes.  In building construction you’ll find standard and uniform sizes from building to building. Door jambs and wall studs for example.

So, the hardwood industry standard for indicating the size starts with lumber thickness, and it’s expressed as a fraction: 4/4, 5/4, 6/4, 8/4 and so on.

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 explain more, starting 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 Monday, April 28th, 2014 at 11:54 am and is filed under Tips and Tricks, Woodworking 101. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.

  • lrick

    Do you suggest I use 4/4 or 6/4 knotty alder to make a hanging barndoor?

    • http://www.woodworkerssource.com Mark Stephens WWS

      The hardware you use will probably have a specification for the thickness of the door, so get your hardware first. Usually interior doors for closets and passage ways are 1-1/4″, 1-1/2″ or 1-3/4″ thick. So you’re most likely looking at using 6/4 or 8/4. But still, get your hardware first and that will probably answer the question with certainty.

      I’d like to see a picture of this door when you get it done!

  • Weatherby

    I’m planning to buy my own portable sawmill, so I have to become familiar with the terms. This information makes it much easier to understand. Thanks

  • pstem

    can you explain E4E

    • http://www.woodworkerssource.com Mark Stephens WWS

      E4E means Eased 4 Edges. It’s a term that often describes a decking product. When they say the edges are eased that means there’s a slight round over along the length of the corners of the board, which is a good thing for decking. In this attached picture you can see there’s a very slight radius on the corners of all 4 edges. That’s E4E.

      • pstem

        Excellent and thanks… the reason I am inquiring is… I export cants of precious hardwoods from Nicaragua of that have been downed by hurricanes Mitch and IDA. Amazing wood that is difficult to extract but as well very hard to find in the market due to the protection in place for these species. The new law states that timbers must be touched at a minimum on 2 sides by industry-mill before export. No more chainsaws with marcos in the jungle. I respect the law and there fore have changed the business plan and bought a mill. The mill is an existing mill and all the machinery is from Austria. Including a KD environment. I have now opened the market and now am receiving the requests to deliver S4S – E4E – FAS decking.

        Is there an industry standard to the roundness of the edges with regards the E4E.

        • http://www.woodworkerssource.com Mark Stephens WWS

          I don’t know what the standard radius dimension is, sorry. Decking industry is a little out of my field of knowledge. If you’re getting requests for the material, your customer may know.

  • DD

    Does 5/8″ thick finish lumber come 11 1/4″ ? [12" Nominal] My Interior stairs need 5/8″ material for “skirt board” each side to transition smoothly to 5/8″ x 5″ base trim at top and bottom? Appreciate any comments.

    • http://www.woodworkerssource.com Mark Stephens WWS

      Probably not. You’d have to plane it down from 3/4″ thickness. If you don’t have that capability it can be done by a milling service.

  • Elton

    Thanks great easy to understand article and I appreciate the knowledge. So I am planning t build some shelves for an audio rack I own that came with MDF. I want 3 inch thick shelves. They are about 18 in by 22 in wide. Would it be better to buy 12/4 wood and cut a solid board to the correct size and shape or glue a few smaller 12/4 boards together together to get the size or to glue a series of 4/4 boards together to get the right size and then cut the shape? I do know the wood can curl and also shrinks and expands with the weather.

    Also, the two front corners will have to be concaved inward to fit around the posts. Would it be best to route and with which blade? I do have a router but no routing table. I also have a jig saw.

    I built shelves once before but I used pine which is too soft and to get a thicker shelve I glued two shelves together which doesn’t look anything like the shelves I’ve seen other make. Thanks.

    • bb

      If you have clamps to glue it it would probably be cheaper to glue together thinner boards.

    • http://www.woodworkerssource.com Mark Stephens WWS

      I’m wondering why you want the shelves to be so thick. If it’s only for the appearance, then a better approach is to make boxes 3″x18″x22″ from plywood. Be sure to orient the face veneer so the grain runs the direction you want on the front of the shelves. To notch the front corners, make a template that matches the curved shape and use it to to mark a line on your shelves. Rough cut it with the jigsaw, then clean up with the hand held router and a pattern bit – or just clean them up by hand with a cabinet scraper and/or sanding. Depends how big the curved notch is.

    • the blood brother

      I would build them hollow, with either veneered ply or natural wood, but it will save you money and be lighter than a solid chunk of wood.

  • Mike in Wickenburg

    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?

    • http://www.woodworkerssource.com Mark Stephens

      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.

  • juegos en hospitales

    Hello my friend! I wish to say that this post is amazing, great written and come with approximately all vital infos. I would like to peer extra posts like this .

  • SR

    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!

    • http://www.woodworkerssource.com Mark Stephens

      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.

  • Raiders

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

    • http://www.woodworkerssource.com Mark Stephens

      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.

  • Zak

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

  • Tg

    Very helpful! Thanks

  • matt

    what about a composite material