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Comment by sokoloff | Hacker News Reader

Glad to learn about cutlistoptimizer as I looked casually for something like that in the past. I’ll have to figure out how to feed it from Fusion360.

Also interesting to learn that Japanese “2x4”s are in that ratio exactly. In the US, they’re 1/2” under nominal size (so 1.5” by 3.5”). Makes it awkward to stack pieces together at times. (2 2x2s next to each other in the US are smaller than a 2x4.)

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I knew about the smaller 2x4s, but now I have a sudden irrational anger that the 2x2s are not also smaller...

How 2x4s depreciate according to Twin Peaks: [0].

It appears in the US they start out at 2x4 and are trimmed down to make them look more finished.

[0]https://m.youtube.com/watch?v=txPcLOtbG3s

EDIT to ask if OP means 'bigger' rather than 'smaller'?

I meant smaller. A US nominal 2x2 piece of framing lumber is 1.5” x 1.5” (for the same reason a 2x4 is 1.5” x 3.5”)

If you still want to have anger, you can take solace that 2 1x2s do stack up to be (very close to) a 2x2, but 2 2x2s do not make a 2x4.

https://www.archtoolbox.com/materials-systems/wood-plastic-c...

Actually, 2x2s are often or usually 1⅜" x 1⅜", which is rather annoying at times. I'm not sure if that has always been the case, but these days they're mostly only available in finger-joint spruce/fir/pine (presumably from offcuts of larger sizes), which might have something to do with it.

(Unlike solid 2x2s, which tend to twist and warp so much as to be completely useless, finger-joint 2x2s are super stable, and always come dead straight.)

Is there a sane explanation for why 2 = 1.375?

Just a guess, but it's probably because the finger-joint boards are made from short offcuts from the manufacture of larger boards like 2x4s joined together with long zigzag joints. Saw kerfs and finishing sanding probably account for the ⅛" difference in size.

It's usually not a problem, except when it's used beside a 2x4 on the flat, in which case the 2x4 needs to be thinned down on the table saw.

Lumber mills used to separate sawing and milling, so the roughsawn 2"x4" might have been about that (+-5 mm or so), but if you mill that square and (relatively) flat you're loosing a bunch of material. The milled lumber probably still got called 2"x4" since it was made from that. And then things shifted to milled lumber only, and the dimension change stuck.

Mills cut 2x4 to whatever size close to that then machined it to dimension. Some did a final dimension of 2x4 exactly (within tolerance), others did other sizes. Once you started building something you had to buy everything from the same mill. In some areas this wasn't possible as the yard you bought from changed suppliers.

Eventually they decided enough and standardized on the current size. The standard is more important than the actual size.

I'm curious how the difference came about. It seems likely enough that a standard was written and then processes improved to the point where essentially everything was at the small end of acceptable. But maybe it is just the drying and trimming.

To address the various questions about the origin of 2x4 sizing, Here’s a brief article on the topic (TL;DR: incremental reductions over decades until standardization was imposed in 1964): http://www.harvarddesignmagazine.org/issues/45/nominal-versu...

I had been told it had something to do with WWII but could find no actual evidence.

When we remodeled our house (built in California in 1920j We found all the 2x4s were 2x4, all the 4x6 were really 4x6 and all had been cut from the center of old growth trees (no knots and no warping after 80 years. We reused them all of course.

The quality of lumber in early 20th century houses is incredible. You'd go broke trying to build a modern house out of lumber that good, assuming you could source it in the first place.

Meanwhile, my 6x6 deck posts are actually 6x6 and a 2x6 railing won't cover it.

Use 2x8 ripped to size :-)

You must have either bought some kind of fancy 6x6 or something. A standard 6x6 is actually 5 1/2 on each side, same as a 2x6 width.

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