Help with Common Metric Sizes?

[wow]

I am about to build my first all-metric project, which will be the stand for my Kapex. I am trying to embrace the whole metric idea, which means I need to think metric from start to finish. In order to do that, I need a little help understanding something that is undoubtedly second nature to those of you who grew up with the metric system - common or standard sizes.

For instance, here in the US we have common dimensional lumber, i.e. 2x4, 2x6 etc. Even though a 2x4 isn't '2 anythings' by '4 anythings', I have learned what it is and how to use it efficiently.

And sheet goods are typically 4' x 8', so I know how to maximize a build and minimize waste with them as well.

But when it comes to the metric stuff, I'm mostly lost. I know about the 32mm system, of course. And I know that a sheet of Baltic Birch is typically 1525 mm x 1525 mm, or just over 5 feet on a side. But therein lies the rub:

Why 1525mm instead of - say - 1500 or 1600? I guess I mean 'why' as in 'why aren't the sizes some nice round number like 1600mm in the example above' instead of the random insanity of the US dimensional lumber sizes? I was hoping that the metric system had managed to avoid the that. Guess not?

So, help me understand some Metric Basics:

32mm system - logical and intuitive. Check!

Panel thicknesses:
3 mm ≈ 1/8″ (3 plies)
6 mm ≈ 1/4″ (5 plies)
9 mm ≈ 3/8″ (7 plies)
12 mm ≈ 1/2″ (9 plies)
18 mm ≈ 3/4″ (13 plies)

also logical and intuitive. Check!

Panel size (that I know of) 1525mm x 1525mm. Not logical or intuitive, but I can learn it. This is an example of what I am talking about and need to learn. What other 'basics' should I learn for my move to thinking metric?

Feel free to point me to a good resource instead of feeling like you have to type a whole chapter that someone else has already covered. i'm willing to go read and learn on my own...I just need to be pointed in the right direction?

Thanks in advance!

 

[jonny round boy]

Why 1525mm instead of - say - 1500 or 1600? I guess I mean 'why' as in 'why aren't the sizes some nice round number like 1600mm in the example above' instead of the random insanity of the US dimensional lumber sizes? I was hoping that the metric system had managed to avoid the that. Guess not?

The simple answer is that 1525 is the metric equivalent of 5'. Nothing more to it than that. Same as the reason other sheet materials are 2440 x 1220, because it's 8' x 4'.

There's no reason why sheets should need to be made to a nice, round number. You generally want raw materials to be slightly oversize anyway, so you can trim them down to get rid of any damaged edges.

 

[RC]

I guess the panel sizes differ between NA and Europe. Here a standard sheet of ply is 2440x1220 or 3000x1500. I guess the uneven one is somehow related to imperial sizes and the even one is more European.

 

[RC]

I guess the panel sizes differ between NA and Europe. Here a standard sheet of ply is 2440x1220 or 3000x1500. I guess the uneven one is somehow related to imperial sizes and the even one is more European.

Come to think of it 3000x1500 is quite exactly 10'x5'

 

[wow]

I guess the panel sizes differ between NA and Europe. Here a standard sheet of ply is 2440x1220 or 3000x1500. I guess the uneven one is somehow related to imperial sizes and the even one is more European.

Thank You, Reiska, and also jonny round boy.

The fact that 2440x1220 is 'soft' metric for a 4x8 sheet makes sense. I will learn those numbers.

And the 'hard' metric size of 3000x1500 seems perfectly logical and is the kind of sizing I would expect - but have never heard of. Is this a truly common size - would it be available at the UK equivalent of a home center, or a lumber yard? Or would you have to get it from an industrial supplier?

 

[jonny round boy]

No, you wouldn't find 3000 x 1500 sheets in a DIY place, or even most trade places. You'd need to go to a specialist panel supplier.

 

[elfick]

Come to think of it 3000x1500 is quite exactly 10'x5'

I had to scratch my head about this for a minute until I realized you were using 25mm per inch. Isn't the exact conversion 25.4mm = 1in?

 

[jonny round boy]

1500mm is just over 59", almost a full inch short of 5'.

 

[Dunn wood]

It is 25.4 = 1 inch
This is what I use:
305 = 12"
610 = 24"
915 = 36"
All common cabinet sizes, everything else is a free for all.
I build all my cabinets in metric and assemble with Domino, which has a metric scale on it.
Secondly get an all metric tape, combination are too confusing.
Took me a while to get used to it but now it is sooo easy

 

[Kev]

Turn your name upside down and remove the "o". Done [wink]

 

[wow]

Turn your name upside down and remove the "o". Done [wink]

Cute!

 

[Mickfb]

Building trade here in the UK still mix imperial with metric.

 

[Stone Message]

The sheet sizes persist because of the machinery in the various parts of the world where sheet goods are made. The machinery often dates back to the imperial days and is so well made that it is still going strong today. Then the handling equipment is designed to match the 8' x 4' or 5' x 5' sizes and so it goes on. If you look at the design of the van industry you will find more designed and optimised for the carriage of 8' x 4' sheets than you would otherwise credit.

I had to do the transition from Imperial to metric having been taught pounds feet and inches and pounds (money), shillings and pence. You just have to do it. I found it easier at the start to have a tape rule that had both metric and Imperial side by side. Many are still like that in the UK. Now I avoid Imperial as much as I can as I feel completely at home with the standard.

The great thing is that I can (even at my age) do the maths for metric (adding, subtracting, divisions and multiplication) so much faster than I was ever able to do with Imperial units. Not only that but I make less mistakes and my work is far more accurate. I generally work to the nearest 0.5 mm but my tools are all capable of 0.1 mm settings which really does help.

Peter

 

[RC]

I just used approximations off the top of my head 1 foot = 30cm and went from there.

Also 24" = 600mm in my mind for all intents and purposes for cabinet sizing even though its obviously slightly off.

 

[Sparktrician]

Start thinking in increments of 32mm. 

 

[wow]

Start thinking in increments of 32mm.

I am trying. To that end I made up the following chart to help get a feel for metric sizes.

[attachimg=1]

For instance, I now know that 600mm is 'roughly' 2 feet, 1200mm is 'roughly' 4 feet, etc. I won't be doing a conversion to imperial in my head each time, as that would defeat the purpose. But starting out NOW knowing that 1200mm is about 'this big' (he holds hands apart to approximate 4 feet) I can start to 'think' in metric numbers that mean something to me.

 

[Sparktrician]

Start thinking in increments of 32mm.

I am trying. To that end I made up the following chart to help get a feel for metric sizes.

[attachimg=1]

For instance, I now know that 600mm is 'roughly' 2 feet, 1200mm is 'roughly' 4 feet, etc. I won't be doing a conversion to imperial in my head each time, as that would defeat the purpose. But starting out NOW knowing that 1200mm is about 'this big' (he holds hands apart to approximate 4 feet) I can start to 'think' in metric numbers that mean something to me.

Wayne, you've been getting inside my head again!!!  Your chart is eerily like one I've been using.  Just converted it to a PDF. 

 

[wow]

Wayne, you've been getting inside my head again!!!  Your chart is eerily like one I've been using.  Just converted it to a PDF.

I believe the saying is "Great minds think alike!"

[not worthy] [thumbs up]

 

[bkharman]

Trying to think in mm is the tricky part. Our brain is wired to do that. Same thing goes for foreign languages... Thinking in that language is the "final chapter" in adopting it.

I started thinking metric (really only mm at this point) by doing this. You are most likely doing the first step as it involves looking at a board and guestimating  how long/wide/thick it is. Just start trying in mm now.

If you find that you are pretty close, the learning curve should be pretty easy. If not, you will get better with time. I feel that this is also a lot like teaching children sight words...  It is just something you have to burn to memory.

 

[tjbnwi]

19 mm is (closer) to 3/4".

0.748031" for 19 mm- 0.750" for 3/4"

Tom