# Plywood standard…



## Oberon_1 (Nov 14, 2015)

Maybe this topic had been discussed before, but I couldn’t find a direct answer.
My question is about the manufacturing standards for plywood. In almost all cases plywood thickness comes rated as a rounded number: 1/4”, 1/2”, 3/4”…But in reality all of them are significantly thinner. For example the 1/4” plywood is 5mm, while the 3/4” is only 18mm thick. That is a significant difference. Therefore the question is why?
And, is there any kind of plywood that is made true to size and if so, who sells it?
Also, there doesn’t seem to be a standard about the number of ply for any thickness. At least it’s never specified in stores and in lumberyards.


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## DesertRatTom (Jul 3, 2012)

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.


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## Oberon_1 (Nov 14, 2015)

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.


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## DesertRatTom (Jul 3, 2012)

Oberon_1 said:


> 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.


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## DesertRatTom (Jul 3, 2012)

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.


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## jw2170 (Jan 24, 2008)

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


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## Oberon_1 (Nov 14, 2015)

DesertRatTom said:


> 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.





DesertRatTom said:


> 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.


You’re right. Anyway, I read somewhere that plywood made to the full size of 1/4”, 1/2”, etc can be purchased. Do you know about such products?


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## MEBCWD (Jan 14, 2012)

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.


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## DesertRatTom (Jul 3, 2012)

Oberon_1 said:


> You’re right. Anyway, I read somewhere that plywood made to the full size of 1/4”, 1/2”, etc can be purchased. Do you know about such products?


Never found any in the usual places, but I bet you can find a big lumber supplier who will have it or can order it. I live in the desert now, and my supplier is an hour's drive away, and so far as I know, they only have Baltic Birch ply in metric, 5x5 feet square. 

l think 2x and 4x is actually 1 5/8ths and 3 5/8ths, which is to say 41.28mm and 92.58mm. To confuse us all even further, lumber is sold by the board foot, which is 12 inches square by one inch deep. Don't know how they sell it in metric countries, but the metric equivalent is 304.88 mm square, by 24.50mm. 

Out in the shop I have a mesuring stick that's one meter long, with both metric and Imperial numbers on the same face, so I can, if needed, just look and see how long a metric measure is in inches and feet. I do think metric is easier in most ways, but I can't visualize a meter and think of it as a "fat" yard.

I found this on the web. It's a conversion chart. Detailed down to 32nds of an inch.


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## mveach99 (Nov 18, 2021)

DesertRatTom said:


> Never found any in the usual places, but I bet you can find a big lumber supplier who will have it or can order it. I live in the desert now, and my supplier is an hour's drive away, and so far as I know, they only have Baltic Birch ply in metric, 5x5 feet square.
> 
> l think 2x and 4x is actually 1 5/8ths and 3 5/8ths, which is to say 41.28mm and 92.58mm. To confuse us all even further, lumber is sold by the board foot, which is 12 inches square by one inch deep. Don't know how they sell it in metric countries, but the metric equivalent is 304.88 mm square, by 24.50mm.
> 
> ...


The 1 5/8 x 3 5/8 hasn't been used for 40 years. It's been 1/2 x 3 1/2 for years now. 1x lumber used to be 13/16 also.


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## MarkJonesRanger (Aug 14, 2020)

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!


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## OldCurmudgeon (Feb 25, 2012)

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-...619&sprefix=plywood+router+bits,aps,65&sr=8-3) which I found to be close enough for my work.


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## J0seph (Dec 2, 2011)

DesertRatTom said:


> Never found any in the usual places, but I bet you can find a big lumber supplier who will have it or can order it. I live in the desert now, and my supplier is an hour's drive away, and so far as I know, they only have Baltic Birch ply in metric, 5x5 feet square.
> 
> l think 2x and 4x is actually 1 5/8ths and 3 5/8ths, which is to say 41.28mm and 92.58mm. To confuse us all even further, lumber is sold by the board foot, which is 12 inches square by one inch deep. Don't know how they sell it in metric countries, but the metric equivalent is 304.88 mm square, by 24.50mm.
> 
> ...


I own a cabinet shop. When ordering plywood for a job I must specifi domestic or import. Domestic is imperial measure and import is metric. The domestic plywood has much thicker outer veneer than the import, sometimes as much as 3 time the thickness. TRhe core veneers are usually better wood in the domestic and the domestic is less prone to warp. It really depends on what you are making. That being said, the domestic is about 25% more in cost.


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## OldCurmudgeon (Feb 25, 2012)

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.


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## J0seph (Dec 2, 2011)

OldCurmudgeon said:


> 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.


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## Micah (Oct 11, 2010)

Oberon_1 said:


> Maybe this topic had been discussed before, but I couldn’t find a direct answer.
> My question is about the manufacturing standards for plywood. In almost all cases plywood thickness comes rated as a rounded number: 1/4”, 1/2”, 3/4”…But in reality all of them are significantly thinner. For example the 1/4” plywood is 5mm, while the 3/4” is only 18mm thick. That is a significant difference. Therefore the question is why?
> And, is there any kind of plywood that is made true to size and if so, who sells it?
> Also, there doesn’t seem to be a standard about the number of ply for any thickness. At least it’s never specified in stores and in lumberyards.


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


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## steveonmars (Oct 26, 2012)

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?


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## jw2170 (Jan 24, 2008)

Supposed to be 2400mm x 1200mm.


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## Wildwood (Aug 14, 2010)

In S.Africa 2440mm x 1220mm


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## mgmine (Jan 16, 2012)

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 "?


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## steveonmars (Oct 26, 2012)

Wildwood said:


> 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.


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## steveonmars (Oct 26, 2012)

steveonmars said:


> 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.


Sorry, 1220mm divided by 3, not 4. It's 4 studs but 3 spaces between them. I divided right just wrote it wrong!


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## Wildwood (Aug 14, 2010)

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.


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## Biagio (Mar 2, 2013)

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?


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