2×4 Lumber Sizes – The History Behind the Mystery | Hacker News Reader

2×4 Lumber Sizes – The History Behind the Mystery

workingforest.com

31 pointsNoRagrets41 comments

2x4s are one of the only things I can think of whose entire name is just literally raw dimensions, so finding out they are not even right was a real wtf moment.

If you’ve ever done construction work (particularly framing obviously) you tend to realize it very quickly, but you get quite used to dealing with it; it’s all quite standardized, simple carpentry.

A lot of batteries like 18650’s or CR2032’s as examples are basically just their size in millimeters, and as far as I know, they are accurate.

Just wait until you find out about the quarter pounder. :)

Aren't those supposed to be a quarter pound before cooking?

I ordered a quarter pounder at a McDonald's drive through, and the cashier said, "There will be a wait on that." I asked, "Oh really? How much will it weigh?" There was a long pause, and they finally said, "About 5 minutes."

This is an A+ dad joke, you should be proud.

The precook weight used to be 4oz (1/4 lbs) but is now 4.25oz, which, I mean, all told, isn't all that different.

kind of like the footlong from subway

I thought they were supposed to be 12 inches long but for whatever they didn't end up that way. That's slightly different than a piece of wood that's supposed to be smaller than 2x4

Edit: apparently there was a class action lawsuit but it found that by and large the bread is 12 inches: https://www.forbes.com/sites/ericgoldman/2016/02/29/why-the-...

They're longer than my foot so I'm getting a deal.

Why is 24/7 "anytime" Pizza only open from 10:00 PM - 4:00 AM on weekdays or 11:00 PM to 5:00 AM on weekends?

https://www.247pizza.nl/contact

I went down the street to the 24-hour grocery. When I got there, the guy was locking the front door. I said, “Hey, the sign says you’re open 24 hours.” He said, “Yes, but not in a row.” -- Steven Wright

A couple of years ago there was an urgent care clinic near me that put up a big banner that said "Now open 24/7" and in smaller letters underneath, "Closed Sunday, Monday, and Thursday". Presumably they had a novel definition of "/7".

Plywood has entered the chat

The 3/4" plywood I get is 3/4". But there's a lot of 11/16" plywood. It makes a big difference when repairing subfloor.

23/32” is quite common, to the point where they make sets of 1/32” undersized router bits for cutting slots to fit undersized plywood

https://www.woodcraft.com/products/freud-89-670-3-piece-unde...

  - Creates perfectly fitted grooves and dadoes
  - Ideal for 1/4" to 3/4" plywood
  - Includes 7/32", 15/32", and 23/32" diameters

Have faith in 8020.

Is that mm?

Well, 20mm x 20mm, now I'm wondering about the 80...

Seems a bit strange it was never rebranded... We just buy structural timber by its actual dimensions (the standard here is 90x45 mm) here in Australia.

if we (America) ever actually finish migrating to metric that might actually happen, but 1 1/2" x 3 1/2" just doesn't roll off the tongue.

I find it interesting that it's not 45x90mm.

For a lot of applications, you can assume thickness, so width is usually the headline number.

Floating shelves are typically going to be a nominal inch thick, likely planed to around 20mm, so you can tell an apprentice to go and get 2m of 140mm board

Like finding out men's jeans sizes are not actually the dimensions of the waist.

If time counts as a dimension then there's 7-11.

Los of batteries are hmm in some circles purely by their dimensions. 18650s for example.

A4 (paper)

35mm (film)

9mm, 12ga, 22cal (firearms and munitions)

A pint (beer)

A 40 (beer again)

Two four (beer, though it refers to the amount of cans rather than dimensions)

26er (booze)

40 pounder (booze again)

Deuce and a half

Website seems to be suffering from hug of death. https://web.archive.org/web/20231212021652/https://workingfo...

The relevant standard is called PS20, American Softwood Lumber Standard:

https://www.nist.gov/system/files/documents/2021/10/26/PS%20...

Note also that green wood will shrink as it dries, so the moisture content at the time of grading makes a difference.

“The modern-day dimensions of a 2×4 are smaller due to historical practices and practical considerations. Thinner pieces of wood were favored over time to reduce shipping costs and increase efficiency in transportation. These dimensions eventually became standardized to strike a balance between cost-efficiency and structural integrity.”

I guess keep an eye on whether they continue to get smaller over time.. the above is a nice explanation but it could just be shrinkflation.

They certainly seem to get closer to the minimum acceptable ANSI or lumber association standards as computerized mills optimize cuts further.

I always figured it was due to milling to finished dimensions from raw lumber. You can buy unmilled lumber by the board-foot (basically 1”x12”x12”), and you get exact pay for dimensions, but when you’re buying finished, milled lumber the only thing that you can trust is that it’s been milled to a standard.

In other words, they start with ~2”x~4” and mill to exactly 1.5”x3.5”

Don’t ask me why that all changes at 1/2” dimensions.

As long as the lumber is a standard size then it can be accounted for. The problem is that when dimensions get too far from what you need then you have to use more lumber and/or make a lot more scrap, leading to more cost in both material and labor. A lot of things in home building are based upon standard lumber dimensions.

That said, even after building with dimensional lumber for decades, it's still weird to me that a 2x4 isn't 2x4.

I'm just getting into woodworking. This has been a consistent source of confusion. It's no simpler with rough lumber. The usable yield of 4/4 (i.e. four quarter, or a one inch thick rough piece) is at least 13/16 of an inch after surfacing two sides.

> Wood manufacturers faced a significant challenge in the late 1800s when forests near major cities were depleted, necessitating the shipping of lumber over longer distances. However, the exorbitant costs of railroad shipping, often double the price of the lumber itself, prompted manufacturers to find innovative solutions.

There was a book recommended here on HN a few months ago - Nature's Metropolis - that devotes an entire chapter to why and how, in the second half of the 1800s, shipping green lumber to Chicago lumber yards came to dominate the entire industry. Yet that changed very suddenly as the above quote points out.

The TLDR is that within an hour or so of arriving in Chicago, your load of lumber would go to auction, be bought, and you'd have cold hard cash in your pocket. To facilitate this, the Chicago yards all agreed to adopt size and quality standards like the grain elevators had. Other cities paid much more, but took days or weeks and you got a promissory note rather than cash.

But at some point the railroads started charging by weight rather than by carload, and it was worth drying your lumber before shipping. Nobody shipped to those Chicago yards after that, so someone else had to take over the standardization of dried lumber.

I live in a building built in the 40s near Chicago and I've done a lot of work that exposed various parts of the underlying structure, and the history you describe is all over the place. The dimensional lumber in the walls and floors/ceilings are widely varied and rough, not planed to anything too terribly specific. To add further injury built on sand because we're on a dune by the beach, Which as you can imagine means things are never square or plumb :-)

I recently realized that the steel beams in the ceiling of the bar (building used to be a bar/restaurant/inn) are actually old railroad ties or something. Chicago industry baby! :-D

This video does a better job to explain the underlying reasons: https://www.youtube.com/watch?v=WaJFudED5FQ.

That video does exactly the same job explaining the underlying reasons -- down to using much of the same wording, and the same visuals.

And it was online for a few weeks before this article was published.

One even has a watermark and a Youtube seek bar. This was painfully obvious.

If you want real ones, then request metric, 5x10 is always 5cmx10cm.

TL;DR - 2x4 is the rough dimensions, the pieces are planed (have surface material removed) to create a smoother/finished surface on the board and the final dimensions are slightly smaller than 2x4 as a result.

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