What's up with wood dimensions?

[ironhat]

I just bought some 1x8s for a rustic projet and while building noticed something different... the 8" dimension which is really 7.5" is now 7.25". What the heck!! By the laws of rounding up/ down, this should be called a 1x7, shouldn't it? I'm just blowing off here because the old sizing has been the standard of the industry for many (30?) years. BTW, I checked a family run yard too and it was the same. Unfortunately, the guy with a brain wasn't there and I couldn't get an answer any further than, "That's what they sent us". Well, "Duh"!! OK, I'll stop for real, now... grrrr!

[LarryG]

Um ... not sure how to break this to you, but nominal 8" lumber has measured 7-1/4" for at least 35 years. I know this because that's approximately how long ago it was when I got my first job as a framer. A 1x6 or 2x6 and smaller is 1/2" shy of nominal size. A 1x8 or 2x8 and larger is 3/4" shy.

[mschrank]

Don't feel bad, that caught me awhile back as well...I assumed actual sizes were always 1/2" smaller than nominal.

http://www.localbuilders.com/lumber-dimensions.cfm

[Mr__Bill]

Last time I got pressure treated wood the 2x8s were 7 1/4, 7 7/2 and 7 5/8 and a lot of in between sizes. Seems the wetter they were the larger they were. I decided to mount the hangers as if they were all 7.25 and hope they all eventually got to be the same size. I did however start with the smaller and worked to the larger as I went across the deck. May have to go back someday and see just how it turned out.

Bill, who thinks that there is a size matters joke here but won't go there.

[Greg.B]

1 x 7 and above is 3/4" smaller then the amount. 7 = 6.25, 8 = 7.25, etc.

Its good you didn't find the guy with a brain, you might of had an argument with him...lol...

[Slik Geek]

...nominal 8" lumber has measured 7-1/4" for at least 35 years. I know this because that's approximately how long ago it was when I got my first job as a framer.

The nominal sizing was larger before that, right? When I moved a doorway in my previous house (1950 vintage), I had to add "shims" to build up the new 2x4s to match up with the old lumber in the house.

Anybody know when the transition happened? (That transition must have been painful... or did mills slowly reduce the dimensions over a period of years until they achieved their new nominal dimensions?)

[LarryG]

The nominal sizing was larger before that, right?

I think the answer to that is Yes, but I'm not absolutely sure. I've seen quite a few 2x4s that measured 1-5/8" x 3-5/8", typically in buildings 50 or more years old. But I've also seen buildings of about that same vintage with studs measuring a full 2" x 4".

A structural engineer once told me that after computers came along (the kind that used punch cards, not what we all have on our desks), the lumber mfrs were able to more carefully calculate what load a given species of wood could carry at a given size, and that's when they reduced the dimensions to the current standard. It may be that there was no single, common standard before we had what we have now; I just don't know. If I had to guess, I'd guess that the 5/8" fractional size was the standard for at least some period of time, because I've seen a lot of studs with those dimensions.

[ironhat]

1 x 7 and above is 3/4" smaller then the amount. 7 = 6.25, 8 = 7.25, etc.

Its good you didn't find the guy with a brain, you might of had an argument with him...lol...

Ahhhhh, that would explain why I measured all of the other wood purchased and they were 1/2" short of the stated nominal size. I have seldom bought anything over 1x6. Thanks, folks. My head no longer feels like exploding. And, thanks to you, Larry, for not wanting the facts cause me too much anguish - LOL! OK, back to the shop - and I don't think that the wife will notice the difference.

[ironhat]

Eliminating a duplicate

[ironhat]

1 x 7 and above is 3/4" smaller then the amount. 7 = 6.25, 8 = 7.25, etc. snip

Now, theeere's the problem. I can't recall the last time I bought 1x8 material (I don't ever recall seeing any 1x7 stuff around here, Greg) so, this would be new to me. Hey Larry, thanks for being considerate about wrecking my delicate psyche - LOL!! Well, Back to the shop. I don't think the wife will miss that 1/2"... at least, I hope not!

[LCHIEN]

so now the real question is, why have they been screwing us for 35 years?

I though the missing 1/2" was dues to rough vs. finished sizes, the 1/2 was what they took off in planing to final dimsensions.

But obviously, you have to plane a 8" board the same as a 6" board, why the missing 1/4" on boards 8" and up?

[mschrank]

so now the real question is, why have they been screwing us for 35 years?

I though the missing 1/2" was dues to rough vs. finished sizes, the 1/2 was what they took off in planing to final dimsensions.

But obviously, you have to plane a 8" board the same as a 6" board, why the missing 1/4" on boards 8" and up?

The ones screwing us will point out that some of the size reduction is also due to drying. A wider board shrinks more relative to a more narrow board.

Not sure I buy that as a legit explanation, but that's what they'll tell you.

[Uncle Cracker]

OK, back to the shop - and I don't think that the wife will notice the difference.

Mine sure would... (Sorry, I couldn't let a straight line like that one get away...)