What is ...B1 size?
The metric system of sizes which are common in most countries around the world, with the exception of USA and Canada, has been commonplace in the UK since the 1970's. The ISO (International Organization for Standardization) was founded in 1947 and for paper sizes they adopted German DIN (Deutsches Institut für Normung) - meaning "German institute for standardisation" who established the DIN paper sizes in 1922 .
The premise of the system is to fix the size of finished jobs - being A6, A5, A4, A3 etc. Therefore the system works like this:
'A' sizes are intended to be the finished job sizes
'RA' sizes are to allow grip on the printing press, which is then trimmed to give a finished 'A' size
'SRA' sizes allow for both grip and bleed on the printing area, which is then trimmed to give a finished 'A' size
'B' sizes allow for oversize formats (...whatever that means!)
Here is a list of ISO 'B' sizes - but remember they are 'theoretical' sizes:
B0 1000 x 1414mm
B1 707 x 1000mm
B2 500 x 707mm
B3 353 x 500mm
B4 250 x 353mm
B5 176 x 250mm
B6 125 x 176mm
B7 88 x 125mm
So why this whole post about what size is B1? Well basically it is because it causes much confusion ...and the reason is that the B1 size held in stock by paper mills and merchants differ from the 'theoretical' B1 size listed above. I have never come across a mill or merchant in the world who holds a B1 sheet size of 707x1000mm in stock - it simply does not exist!
B1 stock sizes can be 720 x 1020mm,720 x 1010mm, 710x1020mm or 700 x 1000mm — all are regarded as B1 size. This can be confusing and is worth considering if you a specifying a particular paper for a project - especially when considering the finished size.
For example, this Modern House brochure which I wrote about on this blog some time ago, is a finished size of 340x240mm. The Omnia used for the text and cover comes in a sheet size of 720x1020mm but the Colorset, Light Grey 120gsm, which also forms part of the text pages, comes in a size of 700x1000mm. Therefore the finished size of the brochure was dictated by the size of the smaller sheet size. If both sheet sizes had been 720x1020mm, it would have been possible to increase the finished size of the job to 345x245mm.
...and one more piece of advice: it's not a good idea to refer to B4 or B5 as "finished job sizes" - because if people take them literally and look up the 'theoretical' size (as above) you are creating a situation where you can't produce what you have referred to - not without doing it either at a ridiculous cost or subsequently reducing the size.
With thanks to Justin at Push for clarifying some of the points in this post.