I need help with inches, so obviously thought of the Dope

I have a client who sells a wood product around the world - we are their creative agency, so produce a lot of their marketing collateral in both metric and imperial, for EU and US markets.

I’ve been sent some measurements to use on a technical drawing, but the US inches don’t make any sense to me, and the person that sent them isn’t available.

The metric measurements are 32mm x 150mm.

The imperial are given as 5/4 x 6.

I get that ‘6’ means six inches. But what on earth is 5/4?

I have another measurement which is similarly confusing - 4/4 x 6 (25mm x 150mm). Isn’t 4/4 just… 1 inch? It doesn’t make any sense to me.

It’s pretty standard for how wood is sold… 1.25 inches is referred to as “5 quarter”. It’s how I’ve seen it at most lumber yards when selling “dimensional” lumber.

I don’t know what’s your tolerance, but there is some evident rounding off, because 5/4 “international” inches = 31.75 mm. Similarly, 6 in = 152.4 mm.

Surely the precision is supposed to be finer than 1/4 inch, though? Does it say anything?

This website says:

Additionally, hardwood may be sold in quarters . Each quarter refers to 1/4 inch of thickness, meaning that a 5/4 board is roughly 1 1/4 inches thick. If your project calls for a piece that is exactly 1 inch thick, you’ll want to purchase a 5/4 board and mill it down to the proper size using a jointer/planer.

That’s really useful to know, thank you! So it sounds like an industry standard term, rather than a precise measurement.

You may already know this, but just in case (and for the benefit of anyone coming into this thread who isn’t aware), lumber sizes aren’t lumber sizes. A 2x4 isn’t 2" x 4". Subtract a bit for planing, shrinkage due to drying, etc. and you’ll find your 2x4 is closer to 1 1/2 x 3 1/2 inches.

Similarly, in the OP you specify 4/4 as 25mm. It’s actually going to be closer to 20mm.

@DemonTree 's link goes into much more detail.

This is an issue in the U.S. if you are working on old houses. In the old days, sometimes a 2x4 really was 2" x 4".

You might want to confirm that they mean 4/4 rather than 1". From what I know, something like 4/4 is rough cut lumber and would still have saw marks. It’s generally not suitable as is except for things like studs where it doesn’t matter. It would need to be surfaced to be used in things like furniture and cabinets. You would generally end up with 3/4" thick boards from 4/4 lumber. Since they are using both metric and US terms, I’m wondering if there was a misunderstanding that can sometimes happen when listing both units. Find out if both measurements are supposed to be rough cut or finished lumber.

The OP said this was on a “technical drawing”, though. Would lumber sizes be indicated on such a drawing, as opposed to actual measurements?

Maybe. If it’s a spec sheet for something like deck planking, it might say 5/4 x 6 on this “technical drawing” when the actual dimensions would be 1" x 5 1/2". Context matters.

ETA: I looked up an actual spec sheet for a trim board. The board is referred to as 5/4 x 6 x 16’, but then there is a drawing showing the actual dimensions as 0.91 x 5.5 inches.

Yep, that’s exactly what it is - a spec sheet for decking.

For the record, this wood is planed in the EU, so the US sizing is a rough translation of the original (25mm). There’s a note on the drawing which stipulates ‘actual’ vs ‘nominal’ dimensions, which may account for the differences you’re discussing.

Something else that one may not have encountered:

We bought some carpet at Home Depot some years back. We needed 14 feet x 12 feet, 10 inches. While the clerk was calling HD Central to place the order, I scanned the order form and noticed 14 x 12.10 for size. I made a bit of a stink, and rightly so, about the terminology – did 12.10 mean 12 feet and 10 inches or did it mean 12 and 1/10th feet? it took awhile to get the clerk to understand, but she made some calls and found out HDC understood it as 12 and 1/10th feet, meaning the carpet would be over 8 inches short. Corrections were made.

Wonder how many other customers have short carpet in their homes?

There was an entertaining Straight Dope column on lumber sizes

For the OP - be grateful you weren’t ask to translate wire gauges. I had to do that once and turns out every country has its own way of expressing that, sometimes multiple systems, based on early industrial history where private companies just made it all up as they went a long. They don’t convert cleanly.

If it is that, then those boards are used as is, they don’t get planed to a different dimension.

If this is made by a European company, then the metric measurements are almost certainly correct, but it could be that they just translated to American units without fully understanding subtleties like the measurement of planed vs. unplaned lumber. Or, given the notation of actual, not nominal, measurements, it could be that they know just enough about such subtleties to know that they don’t want to deal with them. Whether any American lumber company actually sells lumber in those actual dimensions or not isn’t their problem.

I just took delivery today of a load of “5/4 x 4 tongue and groove” hardwood deck boards. ‘(Approx. Finished Size: .94”+/- x 3”)’

Lumber listed in quarters is rough dimension. It’s either sold rough or, if it’s been milled, it’ll be smaller than spec’ed.

Pipe sizes were another one. Around here, a 1" pipe had a nominal 1" internal diameter, which, given wall thickness, translated to a fixed external diameter, which had to match the internal diameter of pipe fittings. But as technology improved, wall thickness shrank. The fixed external diameter couldn’t be changed, so the actual internal pipe diameter increased: a 1’’ pipe was a name, not a measurable dimension.
Metrification reset everything, so a nominal 25mm pipe is now recognizably close to 25mm.

They’re an international timber company with offices in the US, I think they know what they’re doing.

And there are two different sizes of PVC pipe that are both called “half inch”. One has an inside diameter of 15 mm, presumably due to the effect you describe, while the other has an inside diameter that’s actually half an inch. So far as I can tell, there’s no difference on the labels that makes it clear which is which-- You just have to be able to recognize them (the examples I’ve seen have been different colors, white for the 15 mm and yellow for the true half-inch, but I don’t know if that’s consistent).

The Dope is a great place.

Just throwing an additional tip in here: there are “nominal” lumber sizes, yes. “Nominal” in this case means the size is effectively a name rather than a dimensional value, and the word comes from the same Latin root as “name”. However, a warning! Many people use “nominal” to mean “small”. I think they confuse it with the similar sounding “minimal”. So, be on the lookout for this occasional point of confusion.

Are these survey inches or international inches?