Metric is an Imperial Nightmare - No Standard in sheet sizes FML

Discussion in 'Carpenters' Talk' started by FIXMAKEBUILD, Sep 9, 2020.



    I read a few different topics on Sheet goods sizing and I'm none the wiser, I am building a timber framed workshop on top of a 3 course breeze block wall, so I've been potching around on google sketchup making sure i got all my measurements correct.

    My plan was to follow best practices for my building and use 600m centres, Admittedly I'm not a carpenter or tradesman but i can handle my own when it comes to simple framing and building work, years of being to skint to pay such talented individuals has forced me to learn these trades to some level of competency.

    So i get all my timber delivered today, invoice says
    22 x OSB3 9m 1240x1220 sheets when measuring them they are 2400x1200
    20 x OSB3 18mm 1240x1220 sheets, when measure that's what they are

    I phoned my timber merchant to query and they said that's just how they come. no real help at all

    To be clear i ordered these sheet goods to use on 600mm centres, i have ordered trusses all based on this principle, I am confused as to why they sent some that are oversized? i am guessing its something to do with the imperial 16inch centres of old?

    Pretty confused through this whole process, surely now in this day and age we accept that metric is the norm, why are there still imperial sizings in sheet goods, i will have to trim every OSB sheet to fit the 600mm centres i planned on. admittedly its really not the end of the world but why cant we all just agree that metric is here to stay and everyone try to get onboard.

    Sorry if this upsets some you trades people but for the home DIY'er all these different standards are so much to take in, Even ordering screws is a nightmare for me as im stuck between half know imperial and half knowing metric, i even bought a metric only tape because i never know which bloody line to look at lol.

    Rant over
  2. Jord86

    Jord86 Screwfix Select

    How tall are you? What's your waist size? What size doors do you have in your house? Do you order 568ml of beer at a pub or a pint? Don't agree with you I'm afraid, in my experience people only moan about imperial sizes because they aren't capable of simple fractions or common sense, that's not saying you aren't. I use both every day in my job and I far prefer using imperial to metric, at least in the confines of a tape measure, not talking about hectares or whatever.
    WillyEckerslike likes this.
  3. WillyEckerslike

    WillyEckerslike Screwfix Select

    I honestly haven't looked these up
    2.471 acres/hectare
    1.196 sq yards/sq metre.
    It's just something you learn. I do sympathise with the OP though and understand the grief it's causing. It's not helped by builders merchants referring to an 8x4 sheet of plasterboard either.

    I have to confess that I haven't the foggiest how many stone I weigh but I do know that I weigh too many kilos...
  4. Shytot

    Shytot Active Member

    I think OP has a fair point . We did a job in spring , we framed in between steels with 6x2 (x 150x50) @ 16” centres to suit 8’x4’ OSB boards exterior . On the internal of the house plaster boarded have to be now cut to suit ...
    You are right that we still speak and deal in imperial but for me this needs to be phased out , poor apprentice at work is totally confused - “ pass me some 4x2 , oh and some 60mill screws “
  5. I tend to use imperial for timber and sheets and baking, it gets complicated trying to put sheet materials sold in metric in my imperial food mixer :D

    Joking aside, with me its imperial for timber and sheets, measuring up, baking and a few other things, I use metric for electronics, pcb design and enclosure fabrication, Mrs Tux uses imperial for fabric stuff and metric for card making, unless the design of whatever uses metric then I'm asked ' how many of those go into one of these'

    I still use yee old school wood yards that use imperial, makes life easier for me, If I am forced by supply issues to buy in metric then my carefully worked out plans go to pot and often redo the plans for metric, this often results in the swear box being lobbed in my direction.

    Edit...spelling, been long day.
  6. ElecCEng

    ElecCEng Screwfix Select

    So you are saying you ordered and were invoiced for 1200 wide boards and they came in at 1220?

    Sheet material is produced in a factory with engineering level precision so should be the size stated; either 1200 or 1220. It’s not like timber which is planed from a nominal size and could be a few mm either way depending on the yard.

    You were not delivered what was ordered; they need to come and take it back. Next time phone and ask if the 1200 is an exact or nominal size.

  7. Jord86

    Jord86 Screwfix Select

    I use metric for kitchen fitting and setting out cut roofing, imperial for pretty much everything else and I know an inch isn't perfectly divisible by three being as it's 25.4mm but anyone who can do their three times table should be embarrassed if they can't at least get roughly somewhere near a comparable measurement between metric and imperial.
  8. Mr Rusty

    Mr Rusty Screwfix Select

    I agree sheet materials is odd - in my experience anything "timber" is 8'x4' - 2440 x 1220 but plasterboard is 2400x1200, 1800x900 etc (although I see I can also get 1220 x 900 in 9mm??) For all our metrication standard door sizes are still imperial, we have never truly gone metric and so many things are still imperial but with "metric" sizes. At work we use 38mm, 51mm and 76mm hoses - 1 1/2", 2" and 3" in old money. All complicated by "nominal" sizes - don't rely on 100x50mm PAR timber to be anything near - quite likely 95mm x 45mm and of course, always called 4 by 2's :D

    And, as an aside, I've found the same issue planning a garden building - SIPs seem to be 1200 x 2400 and OSB is 1220 x 2440...
    Last edited: Sep 10, 2020


    I have read all your comments and i would like to say i would love to use one measuring system or the other but there is no happy medium, sometimes its metric sometimes its imperial converted to metric, but this doesn't help anyone surely? i can convert inches to metric but we are still left with either cutting down material or using multiple suppliers to get what you need i live in the sticks and getting any reasonably priced lumber is expensive unfortunatley, personally i would love to order from one supplier in a measuring system that is consistent. Perhaps my level of competency isn't what i thought, but trying to piece together a imperial metric puzzle is really confusing to me, i press buttons for a living and have done for 20+ years my main gripe is why in this day and age cant manufactures standardise their products so this conversation needn't be had at all.

    You are right the supplier has provided me with materials that are not as described, should i really complain though? im not really that guy I'm embarrassed to say. i did phone them however to query and their response was "that's how they come" Its really not the end of the world but surely this is a big headache for all you professional tradesmen to? Trying to be as accurate as possible and not wasteful with material and money which admittedly is retrospective is my goal as well as to have a beautiful 9m x 5m building i have been dreaming of for about 20 years.


    And can someone please for the love of beer and getting wasted tell me categorically what "nominal size" means i looked up the meaning and there is no clear answer to that either! :(
  11. Jord86

    Jord86 Screwfix Select

    It's really a marketing con. As an example, 4x2 is nominally sized, being as it should be 102x51mm but actually by the time it goes through the planer and thicknesser ends up 95x45mm, and is sold as such.
  12. nigel willson

    nigel willson Screwfix Select

    Using stone is a smaller number
    WillyEckerslike likes this.


    So the 2x4 non treated timber i ordered is 38 x 88 which isnt even close to what could be considered old school 2x4 FML trying to make a somewhat accurate 3d model of what im supposed to build is a real challenge, I am learning quite alot though :). The thing is i order timber based on the dimension they give me and then when it comes its off by a margin, granted its not a huge margin but im trying to make a drawing so i can be more accurate than i have been in the past where the redneck carpentry with the that'll do attitude just wont do anymore, i have purchased all new tools to do the best job i can do and its really amazing the things tradesmen take for granted and what is acceptable. im trying to get within 1mm accuracy so perhaps im doing myself a disservice by trying to be so accurate over such a large span.




    this is what i have so far, all criticism welcome, like i said im not a tradesman
  16. Jord86

    Jord86 Screwfix Select

    That's because you ordered CLS not 4x2. 1mm tolerance is admirable but ridiculous, the timber you yourself order isn't machined to that tight a specification.


    I am currently redoing everything because of the delivery of timber dimensions being slightly different and the fact that i never considered that i have to build the workshop from the back to the front due to lack of space around my property. will update you here when i finish so one of you talented individuals can point out any glaringly obvious mistakes im about to make :)


    sorry mate my ignorance is about to show right through, i have no idea what CLS means even :( i have spent over a month looking at the timber merchants near enough to me to get the timber i think i may need. i mean what i have im sure will do the job well enough, starting to wish i got the rough sawn 50x100mm timber now though lol although the block is 95mm wild hence my choice to go with the 88mm and then a 9mm osb3 material which will leave a 2mm over hang on the outside plus the siding material which i have considered but not purchased yet


    i have spent weeks just considering what screws\nails and fasteners i need, it think i might have spent nearly £200 just on those which in my brain is a fair amount of stella
  20. Jord86

    Jord86 Screwfix Select

    Canadian Lumber Stock. It's mainly used for stud partitioning, however you can buy strength graded timber that is machined to the same dimensions and it's still generically called CLS due to the dimensions.

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