Dimensional Lumber Width Change

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Forum topic by Beeguy posted 12-19-2008 10:15 PM 9333 views 0 times favorited 8 replies Add to Favorites Watch
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179 posts in 4276 days

12-19-2008 10:15 PM

Topic tags/keywords: wood question

This is something that has bugged me for a long time and no one I have asked has ever given me a good answer. It came up again when I was joining some 1×10 pine for project that had a strict width requirement.

1×2 through 1×6 nominal boards will lose about 1/2” in width after sufacing. Why do 8” and greater lose 3/4”. I could have really used that extra 1/4” on the last project. I am thinking maybe more shrinkage in the wider boards but I would also think than would result in more random width and not hold to 1/4” difference regardless of the width (8, 10, 12).

Just one of those unknowns that I should probably not waste time thinking about.

Happy Holidays

-- Ron, Kutztown, PA "The reward is in the journey."

8 replies so far

View schroeder's profile


702 posts in 4765 days

#1 posted 12-19-2008 11:34 PM

Okay…I know this one….
Lumber (softwoods) is sold on a nominal width. Originally, (until 1911) in the U.S., boards were cut full-sawn rough. That means a 2×4 was a full 2” x 4”. But sizes would be inconsistent from dull/wandering saws in the mills. And builders didn’t like using the rough stock because of the coarseness of rough-sawn and the sharp corners. A governing body (ALSC) set up standardized sizing. The participants included lotsa mill-people along with builders. The mills (I suspect) suggested new sizing to alleviate the aforementioned problems. In their infinite wisdom, they determined the following sizes for green lumber at the mill (there’s a whole other set of sizes for kiln-dried) , after surfacing; A – 2” nominal thickness is actually 1 9/16”
Thicker (4”+) are to the ½”, i.e., 6”x6” is 5 ½” x 5 ½”
Up to 4” nominal widths, the actual width is to the 9/16, i.e., 4” is 3 9/16”
A nominal 2×6 board (dimension lumber) is actually 1 9/16” x 5 5/8”
Over 6” width is sized to the nearest half-inch. So a 2×8 is actually 1 9/16” x 7 ½”, a 4×8 is actually 3 ½” x 7 ½” and so on.
The rules are pretty rigid for sizing and most dimension lumber (framing sizes) has an eased edge on all four edges, timbers/beams generally don’t.
This is all basically a product of sawmills taking advantage during the set up to increase their “overrun”. A mill buys logs (even today) based on log scale (board-feet) which is a set of formulas that determine how many full sawn 2x whatever can be cut from a log. Typical overrun in a good Douglas-fir mill (the difference between log and lumber scale) is over 300%. So if I sell them a log with 100 BF – they will cut over 300 BF of lumber. It’s a crappy system, but we hate change.
Kinda long, but… asked!

-- The Gnarly Wood Shoppe

View Sawdust2's profile


1466 posts in 4727 days

#2 posted 12-19-2008 11:55 PM

Basically, I knew that but you have explained it so that I understood it.

Now if I could just take my 2.x 4 and cut it into a 2×8….


-- No piece is cut too short. It was meant for a smaller project.

View CharlieM1958's profile


16284 posts in 4858 days

#3 posted 12-19-2008 11:55 PM

I think shroeder’s answer contains some good info, but does not directly answer your question.

If you go to Home depot and buy a 1×4, it will be 3 1/2” wide (losing 1/2” from its nominal size. But if you buy a 1×12, it will measure 11 1/4” wide, losing 3/4” in width. Why?

Theoretically, the wider a board is to start with, the greater the odds that the mill will have to take more off to end up with parallel edges.

-- Charlie M. "Woodworking - patience = firewood"

View Dusty56's profile


11856 posts in 4328 days

#4 posted 12-20-2008 12:09 AM

Thank you Charlie for actually answering the question that was asked : ) Happy Holidays to all !

-- I'm absolutely positive that I couldn't be more uncertain!

View dirtclod's profile


169 posts in 4500 days

#5 posted 12-21-2008 11:52 PM

Here’s a document that covers standard demensional lumber sizes.

Mills cut thier lumber taking into account the expected shrinkage of a given specie, the defects expected during drying of that specie, and the final standard demension they wish to achieve. Softwood species use the standard demensions in the above link. While hardwood denensions are more in line with logical thinking.

-- Wonderful new things are coming! - God

View Beeguy's profile


179 posts in 4276 days

#6 posted 12-22-2008 05:27 PM

Thanks for the replys. Glad to know that someone out there is not hording 1/4” strips. :-)

When I am not woodworking I keep bees, which also entails alot of woodwork. It seems no matter where I turn this dimensional lumber thing gets me. Beehives are nothing more than a stack of different size boxes filled with frames where the bees build their honeycomb. The standard size “boxes” use boards that are 5 11/16, 6 5/8, and 9 5/8 inches. As you can see, I have to go to the wider width (and more expensive) board for these. It just bugs me to buy a 1×12 because the 1×10 is 3/8” to narrow.

I am always on the lookout for culls at the lumber yard that I can cut down. However as much as I hate to admit it, it is actually cheaper to by the precut boxes from the bee supplyhouses. I guess they can order special size right from the mill. Kind of takes some of the fun out. I do the beekeeping because I like it and also “for profit” so I have take the cost of materials and time into consideration. But I do have a lot of equipment I made myself when the wood was available.

The size (dimensions) of the hive has been around for 150 years and has not adjusted with the change in lumber. I assume available boards were wider back then. Beekeepers are very resistant to change so if it worked in 1850, we are still using it today.

-- Ron, Kutztown, PA "The reward is in the journey."

View dirtclod's profile


169 posts in 4500 days

#7 posted 12-23-2008 07:47 PM

Back then they either harvested their own wood or went to a sawmill or lumberyard for it. So they ended up with demensions that were more reasonable. You’re going to the wrong places. Check out your local lumber yards and sawmills. The sawmills will have (or can mill to order) rough-cut lumber. Some of the better lumber yards also have rough cut lumber. You’ll find a rough-cut 2×6 will usually measure ~1-15/16” x 5-7/8” after drying.

I can’t remember in all my studies and some beekeeping as a kid but I think I read that balsam poplar, or maybe basswood, was the preferred wood for hives. I’m guessing you’re using pine for the big box stores. Again, I would check with the sawmills and lumber yards in your area. They will usually have rough-cut pine at a price that is equal to the big box stores. Some in your area may have Balsam and basswood. If you want to stay with pine then check out white pine for the interiors.

-- Wonderful new things are coming! - God

View Samel A. Livingstone's profile

Samel A. Livingstone

19 posts in 4231 days

#8 posted 01-07-2009 11:43 PM

I have handling wood since the 1950’s as it was explained to me. lumber was cut over size so when planed was full dimensioned. During WWII drying was a problem and lumber was then cut to actual dimensions. It would then shrink and end up with a smaller cross section. After the war the smaller sizes persistented. 1950’s @ x$’s were 1-7/8×3-7/8. During the next 50 years lumber was progressily shrunk (save Resouces) The 2×4 went to 1-7/8 to 1-3/4 to 1-5/8 to present 1.5 inches. Width followed similar path down to 3.5-inches.

It is frustating to repair or remodlel older homes and not have todays lumber fit to larger stock which was previously used.

Lumber is supposed to be dried before sizing. However if you check lumber at the big box stores it is commonly 20% which is now accepted value for dimensional lumber.

Now if there was a reason for shrinking plywood thickness i would like to know it. How long will it take 3/4 plywood to shrink to 1/2?

-- Sam, upstate

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