Metric Lumber Dimensions

[NW Architect]

Limey Carpenter, or anybody who knows: How do I call out metric sizes of wood trim materials, lumber/timber, and plywood thicknesses. Every site I go to gives a different answer about nominal versus acrual sizes, hard conversion vs soft conversion, and cm vs mm. WTF?

In NOMINAL Imperial sizes I need to call out the metric equivalents of:
1x2
2x2
2x4
1/2" plywood
3/4" plywood

I'm also looking at an architect's plan completely dimensioned in cm, to wit, an overall dimension of this little bungalow is called out "770". Back when I learned metric, this would have been written "7 700". Has that changed?

[dave_k]

we use hard conversions.

2 x 2 = 38 x 38
2 x 4 = 38 x 89
2 x 6 = 38 x 140
2 x 8 = 38 x 184
2 x 10 = 38 x 235
2 x 12 = 38 x 286

1/2" ply = 12.5mm
3/4" ply = 19mm

dimensions are to the mm: 1 meter 20 cm =1.200
55 meter, 521 mm =55.521

[Tom Bainbridge]

NW, i can help with uk construction practice............. i can also give you hints as to european construction practice. i cant help with canadian or american practice

lets nail the centimeter issue first.

uk architects dimension their drawings in millimeters ONLY (thats the required standard since 1968).............. the one thing we got right in 1968 was to avoid ANY confusion

that rule means that ANY dimension number on a uk architects drawing IS millimeters (unless it says otherwise) .......................... you just cant get it wrong

so the drawing you have in front of you (in cm) IS european .......... (or perhaps canadian)

now to trim dimension timber in metric, uk style

first, similar to american practice, the narrow (metric) dimension is always given first {more information would be TOO much}

second, also similar to american practice, the "numbers" for trim timber are NOMINAL {more information would be TOO much}

now to the simple explanation of metric timber and imperial trim timber in the uk, it is funamentally different to american practice

an american sawn 1x2....................... i believe finishes at 3/4 x 1-1/2

not in metric it doesnt

one................ it is sawn at 25x50 (the metric equivilent of 1x2)

two

it looses 5mm (end and side) so ends up finished at 20x45

there is only ONE exception to NOMINAL metric dimensions on trim timber............. building regs (code) for fire doors..........

fire door regs (code) says 25mm thick door stops............ that means 25mm finished. its just one of those cases where you need to know the exception

[NW Architect]

Oh, goody, it IS as confusing as I had feared. Canadian is different from UK is different from European.

So, Tom, the English equivalent of a 1x2 would be called a 25x50 or a 20x45?

The job in question is in Europe - the Balkans to be precise. It LOOKS like finished lumber is called out in mm, but framing TIMBER (which is used rough) is called out in cm

[dave_k]

The job in question is in Europe - the Balkans to be precise.

Can't you get a standard from the country you're building it. You have to apply for permits somewhere, surely they can help. I have a friend who worked in Poland 1992 -94 building agri buildings. He had quite the experience. I remember a story about Soviet electric power trowels with a cord and no safety ring.

[NW Architect]

Tried that. Different answers from different respondents. Language thing

[Tom Bainbridge]

NW you think what i told you above is confusing

to keep things simple (i will answer your specific question)............ it will confuse and amuse you even more :)

in england imperial dimensions WERE always given long dimension first so it was a 2x1

in 1968 when the construction industry went metric, they standardised metric dimensions to always to give the short dimension first so its a 25x50

one thing hasnt changed, the cross section dimensions remain NOMINAL

now the laugh........... and confusion to you, 43 years after the uk construction industry went metric

if i go to the timber merchant and want ten 16 foot lengths of 2x1

i order "ten, four eight, two by ones" (6 sylables)

i dont ask for "ten sixteen foot, twenty five by fiftys" (10/11 sylables)

"four eight" means 4.8 metres

one thing did change when we went metric, 1 foot increments (305mm) became 300mm

hope you remain confused and amused by english excenticity and how we play with words just as much as you guys do :)

[Ted S.]

So when I was back in an architect's office we did some international projects, one was in Oxford, England, another was in Saudi Arabia. They were in metric.

All dimensions on the drawings in all cases were in mm.

I did all my own drawings by gut feeling it in English, then converting it to mm on a Construction Master calculator and rounding it off to even numbers.

Items considered "soft converted" would be a 3' wide door we would dimension as 914mm because the tooling was set up in English.

Items considered "hard converted" would be a 200mm CMU, because the tooling had been changed to reflect metric unit sizes (a soft converted 8" CMU would be 203mm).

In then end it was not any harder than any other project, you just needed a Construction Master.

[Phil Pritchard]

one thing did change when we went metric, 1 foot increments (305mm) became 300mm

hope you remain confused and amused by english excenticity and how we play with words just as much as you guys do :)

Unless, of course, you happen to be framing out for ply cladding under P/B as I recently was. The two Czech joiners working with me couldn't quite figure ot what 16in on centres meant in metric terms, after all 406.4mm isn't that easy to read off a tape. In the wonderful world of metric we have 8 x 4ft (2440 x 1220mm) sheets of plywood, but 2400 x 1200mm sheets of plasterboard. You couldn't make it up

Phil

[Tom Bainbridge]

ted, like you say the construction master is a "good piece of kit" for conversion from imperial to metric

the only additional thing you need to know is the "local" increments

[dave_k]

I did all my own drawings by gut feeling it in English, then converting it to mm on a Construction Master calculator and rounding it off to even numbers.

Items considered "soft converted" would be a 3' wide door we would dimension as 914mm because the tooling was set up in English.

Items considered "hard converted" would be a 200mm CMU, because the tooling had been changed to reflect metric unit sizes (a soft converted 8" CMU would be 203mm).

I've had some very bad experiences with conversions. If you're planning a metric job you have to know what the metric units are and use them. Getting metric and imperial mixed up when building with CMU's is disastrous. There is such a small difference in the block that you don't notice but by the time you get 12 or 16 courses up you have all sorts of problems hitting your grades for openings, red iron, floor heights, openings, stairs... .

Door are another one. Metric doors are built 900 x 1800 which is the equivalent of a 3/0 x 7/0 however a 3/0 x 7/0 is 9/16" wider and 1 1/8" shorter that it's metric equivalent. It may not seem like much but it can be a major screwup on a sizeable job. I have charged more to rework doors and frames than the entire installation contract on jobs where these details are missed. That was just me I don't even want to think what the steel erectors bill was for extras.

If I was drawing up a job to be built in the Balkans I would be making sure I knew what was available as far as standard building materials. It'll take a pretty sharp super to work everything out if you don't. We definitely have a shortage of those in Canada.

[Tom Bainbridge]

phil, you are right

but economics tell you the answer

if you have a stud wall that has (imperial) plywood one side and (metric) plasterboard the other

you frame at 16 inch to suit the plywood because it is 3 times more expensive than the drywall............. its a no brainer

[Tom Bainbridge]

dave_k

REAL metric doors still pain me. i still have to double check them........ and their openings

edit, im used to imperial doors to this very day

................... 43 years after we went metric............ and that was some 10 years before i started work

[Ted S.]

My mother is from England so we had been there often when I was younger.

I had friends there that were "Chippys" if that the correct term?

Anyway, they told me on a jobsite (this was a while ago) that they would get confused and ask for a "4x2...2 1/2 meters long"

I feel for you guys over there...

[dave_k]

dave_k

REAL metric doors still pain me. i still have to double check them........ and their openings

edit, im used to imperial doors to this very day

On commercial jobs we can have either depending on whether the job is drawn up in imperial or metric. You have to look at the suppliers frame or hardware schedule to be sure of what you are getting. I have seen plans written in metric where the doors have been supplied in imperial for whatever reason but it is definitely a mental trip hazard.

Metric block combined with a low bidding mason and a inexperienced or lazy superintendent is a really nasty combination. When you walk into the trailer and they are both squinting at the drawings scratching their a$$es you know it's going to be one of those jobs you wished you never got.