The rest of the world is on the metric system, so no point in manufacturing in imperial as well. Having to reset the machinery that peels, handles, stacks, glues and compresses sheets of ply is fraught with waste and costs. We just have to adapt because imperial fans are a nearly insignificant minority now and the differences are minescule.

I recently found this chart of standards for plywood types and grades. I really use a lot of A-B grade for my projects.

 

1) That is no excuse since a lot is manufactured for the US market.
2) But even if they produce by the metric system, they could say it’s 5mm, or 18mm thick. I’m more annoyed by the fact that it’s advertised (and sold) in fractions of inches, when in reality it’s not.
So, when you buy a sheet of plywood you can’t really tell what will you get (in terms of thickness, number of ply, and what the inner layers are made of). The only way is from previous experience.

 

Imperial sizes are no longer a world standard. We're about the only place left using imperial sizes.

I see using the imperial sizes as a convenience. Massive quantities of metric sized ply is imported to the US. I'm not sure if there is any manufacturer in the USA producing ply. And if they hope to sell it overseas, they will have to produce metric.

Not sure it matters much so long as the makers identify it by its metric size. Calling 18mm 3/4 inch is something done in ad copy and price tags. I don't think there's anything to be done about it. I mean, if you want to use plywood, you don't have any alternatives anymore.

 

I would also like to add, that no plywood is exactly the thickness advertised. A little moisture, or dryness and the dimension will change. That's why we have to buy or make exact fit jigs to cut dados and grooves rather than just buying one or two router bits or fixed with dado sets.

My big issue with metric is that I grew up imperial and I know what a 4x4 should be, but a 100 mm measure is something I have to think about for a few seconds. And how long is a meter? That isn't instinctive to me. A little over a yard, three feet and a nuggie? But my complaints have as much influence as a fart in a hurricane.

 

Even the cutters for making dadoes, are not true to size....

 

If you are having problems with plywood measurements then you should really have problems with solid lumber sizes. If they list it as a 2x4 then it is actually 1 1/2 x 3 1/2.

 

I stopped in to buy some 1/4" birch flooring underlayment to make some boxes out of. 31.00 per 4x8 sheet. It was 13.00 per sheet a little under 2 years ago. I opted out for a storage bag to put the portable wood stove for a canvas tent in and saved $10.00. 43 years ago when I was framing houses our 2x10 floor joists would sometimes need to be cut down as they often had 1/4" to 3/8' difference in width. That was aggravating!

 

AFAIK, The "standard" is 1/32" larger than the actual size. So 1/4" is 7/32", 1/2" is 15/32", 3/4" is 23/32". You can actually buy special "undersized" dado router bits (e.g. https://smile.amazon.com/Whiteside-...ds=plywood+router+bits&qid=1643247619&sprefix=plywood+router+bits,aps,65&sr=8-3) which I found to be close enough for my work.

 

It occured to me that I believe "real" Baltic Birch plywood (sold in 5' x 5' sheets, not the common 4' x 8') is specified with the correct actual thickness. It also has many more layers (I think 13 for a 3/4" vs. 5-7 in regular plywood) and is supposed to have no voids.

 

It is called 1/2" but is actually metric. At least all I have used in the past few years has been.

 

I’ll try to attach a doc I found informative Meet Google Drive – One place for all your files

 

The plywood we buy in the US is a 4' x 8' sheet. Just out of curiosity, what size are they in countries that use the metric system?

 

Supposed to be 2400mm x 1200mm.

 

In S.Africa 2440mm x 1220mm

 

That's almost exactly 4' x 8', just a little over but what do you center your wall studs in construction? We use 16" centers, 4 studs for a 4' wide sheet of plywood, drywall etc. but dividing 1220mm by 4 gives you 406.666666mm. The 2400mm x 1200mm that James quoted makes more sense for construction just because it divides evenly. Again, just curious, I know this thread was about the thickness but my mind kind of wanders a lot.

 

It seems like it would take a lot of effort to write out a shopping list to build something as small as a shed. How would you order an 8' 2x4? And then a 4x8 sheet of 3/4" plywood ripped down to 5' 3 1/2 "?

 

The 2440 x 1220 measurement is the closest rounded off metric mm rendition of an exact 8' x 4', which would be 2438.4 x 1219.2 so it is in effect exactly an 8' x 4'. Most construction in SA is brick, and I know nothing about stud spacing, but perhaps someone else here can comment on that aspect.

 

Like Wildwood says, we do almost exclusively masonry construction, so we know from nothing about framing, studs, etc. Where drywall is used (eg to divide a space) extensive use is made of lightweight steel profiles. The drywall itself is fibre-cement. I have no idea of standard spacing, but plywood is rarely used for this application. Good quality plywood costs a fortune here, whereas drywall or manmade board is more affordable.
Our affordable timber (pine) generally grows too rapidly (large annular rings) to make it either stable or suitable for much other than roof trusses.
I understand things to be different in Australia, where residential construction is more wood-based, but I do not know whether the building technology is the same as in North America. In Australia they can also uplift a house and put it down on another lot - we can't.

BTW, I can understand why the price of good timber is so high here (mostly imported), but what the hell caused prices to spike so much in the USA and Canada?