A Handy Guide to UK Paper Sizes

A Handy Guide to UK Paper Sizes

Paper sizes are something even seasoned print veterans find themselves looking up occasionally. While some paper sizes are used on a daily basis at printers and design studios, there are others that are only used a handful of times a year. Those tend to be the sizes most easily forgotten, so we’ve come up with this handy reference guide that can be referred to any time, 365 days of the year. Don’t forget to bookmark it!

The following is not an exhaustive list of paper sizes, but it should cover the most commonly used sizes used by designers and printers around the UK. For the sake of brevity, we’ll leave out the more rarefied ‘legacy’ sizes that we simply tend not to encounter any more.

ISO Paper Sizes:

You may not have heard of ‘ISO’ paper sizes, but you will have used sizes like A4 and A3 perhaps on a weekly basis. A4, A3, A5, A2, B4 and B5 are probably the most easily recognisable examples of ISO ‘A’ and ISO ‘B’ paper sizes.

ISO 'A' paper sizesISO sizes have several neat, and very handy, mathematical properties about them:

  • The ratio of their sides is always 1 to 1.414 (the square root of 2, by the way).
  • To mentally compute the dimensions from one ISO paper size to the next, you simply keep the longest side and double the shortest. So A4 (210mm x 297mm) becomes A3 (297mm x 420mm). We simply doubled the shortest side (210mm) to get that new 420mm dimension, but kept the existing 267mm dimension — easy!
  • Note that the physical paper size at each step up is DOUBLE the paper area. So A4 is half the size of A3 (fold A3 in half and you end up with A4 again). A3 is in turn half the physical size of A2 and so on.
  • You can alternatively enlarge to the next ISO size (e.g. from A4 to A3) by enlarging the original 1.414 times. So, on a photocopier, for example, you would set the magnification to 141.4%.
  • Most ingeniously, the ISO ‘A’ sizes are designed to allow printers to easily compute the weight of a printed stack of papers simply by counting the sheets. It’s based on the fact that the size A0 is exactly 1 square metre in area. So, if you know you have paper that’s, say, 150gsm in weight (paper is specified in grams per square metre; gsm), you know that a stack of one hundred A0 sheets will be 100 x 150gsm, which is 15000grams (i.e. 1.5kg in weight). If your stack happened to be A1, then you simply need to divide that by two (because, as we learned above, the next A size down is half the size). For A2 you halve it again and so on.

ISO ‘A’ sizes:

The ISO ‘A’ series of paper sizes is most widely used for printing and design in the UK; most people will use A4 paper, for example, on a daily basis. As we mentioned above, each ‘step’ down from one A size to the next is exactly half the size, as you can see in the diagram above/right. Here are the main A sizes:

  • A0 = 841mm x H1189mm
  • A1 = 594mm x 841mm
  • A2 = 420mm x 594mm
  • A3 = 297mm x 420mm
  • A4 = 210mm x 297mm
  • A5 = 148mm x 210mm
  • A6 = 105mm x 148mm
  • A7 = 74mm x 105mm
  • A8 = 52mm x 74mm
  • A9 = 37mm x 52mm

If you want to go larger than A0, the next size up is called “2A0” (1189 x 1682mm). Use the maths trick above to go up from there to 3A0, 4A0 and beyond.

ISO ‘B’ paper sizes:

Exactly as with the ‘A’ sizes, each ‘B’ paper size can be divided into 2 to get to the next smallest size (so B0 folded in half gives you B1, and so on).

  • B0 = 1000mm x 1414mm
  • B1 = 707mm x 1000mm
  • B2 = 500mm x 707mm
  • B3 = 353mm x 500mm
  • B4 = 250mm x 353mm
  • B5 = 176mm x 250mm
  • B6 = 125mm x 176mm
  • B7 = 88mm x 125mm
  • B8 = 62mm x 88mm
  • B9 = 44mm x 62mm

There is also a ‘Super-B’ which is 330mm x 483mm. It’s also sometimes known as A3+.

ISO ‘C’ paper sizes:

ISO ‘C’ paper sizes are usually used for envelopes as they’re ideal for housing ‘A’ paper sizes. So, for example, A6 postcards will fit perfectly into C6 envelopes. Or an A4 sheet folded in half (to A5) will fit into a C5 envelope perfectly.

  • C3 = 458mm x 324mm
  • C4 = 324mm x 229mm
  • C5 = 229mm x 162mm
  • C6 = 162mm x 114mm

On a related note, there is a common size known as ‘DL’. True DL is traditionally exactly one third the size of A4 (so it’s 99mm x 210mm) and generally refers to a paper size. However, when referring to envelopes rather than sheets of paper, the printing industry generally refers to a size of 110mm x 220mm as “DL” size (for envelopes) although technically that size is really called ‘DLE’. The extra few millimetres allow for the enclosed A4 letter or document (folded into thirds) to fit inside with a little bit of slack.

ISO ‘RA’ and ‘SRA’ paper sizes:

These are paper sizes that are a little bigger than their equivalent ‘A’ sizes above. So, for example, RA4 and SRA4 could be described as ‘oversize A4’, although one is more oversize than the other as you’ll see in the table below. The extra area is primarily there to allow commercial printers to print ‘bleeding’ images and graphics up to (and technically off) the edges of the final cut sheets. The additional margin also allows printers to print “printers’ marks” like colour bars, trim marks and registration marks on areas that will eventually be trimmed off, so they’re not visible to the end-user. They need these marks to check ink densities, ink registration and suchlike. Here are the most commonly used paper sizes in each series:

  • RA0 = 841mm × 1189mm
  • RA1 = 610mm × 860mm
  • RA2 = 430mm × 610mm
  • RA3 = 305mm × 430mm
  • RA4 = 215mm × 305mm
  • SRA0 = 900mm × 1280mm
  • SRA1 = 640mm × 900mm
  • SRA2 = 450mm × 640mm
  • SRA3 = 320mm × 450mm
  • SRA4 = 225mm × 320mm

Miscellaneous sizes:

There are a few additional paper sizes that are reasonably common, but fall outside of the ISO paper sizes, so we thought we’d include them here in case you ever need a reminder:

  • Americal ‘Letter’ (ANSI A) = 216mm x 279mm
  • American ‘Legal’ = 216mm x 356mm
  • ‘International Business Card’ size = 53.98mm x 85.6mm although most UK printers tend to round it to 54mm x 85mm.

We hope that this reference for the most commonly used paper sizes is useful for you. Do bookmark this page and share it if so.

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