Paper Sizes & Weights

          

British Imperial Paper Sizes                                                                   

The UK committed to adoption of the metric system when joining the EEC in 1973.  Before metrication the  British Imperial system was used for paper sizes and the most commonly used office writing paper in UK  was Foolscap (or more correctly Foolscap Folio) – 8 inches x 13 inches (203 mm x 330 mm).  Foolscap continued in everyday office use well into the 1980s, causing a good deal of confusion as it was often mistakenly referred to as A4 (210 mm x 297 mm).  For the sake of completion and because the names are quaintly delightful, the following table provides sizes in inches (1 inch = 25.4 mm) of some of the old British Imperial writing paper sizes.

FORMAT DIMENSIONS (Inches)
Albert 4" x 6"
Duchess 4.5" x 6"
Duke 5.5" x 7"
Foolscap Quarto 6.5" x 8"
Foolscap Folio 8" x 13"
Small Post Octavo 4.5" x 7"
Small Post Quarto 7" x 9"
Large Post Octavo 5" x 8"
Large Post Quarto 8" x 10"

 

The A-Sizes

Physics Professor Georg Christoph Lichtenberg wrote a letter in 1786 setting out the case for a height-to-width (or aspect) ratio of the square root of two (√2 = 1.4142).  The German Walter Portsmann studied Lichtenberg’s ratio and in 1918 proposed its adoption to the German Standards Institute (Deutsches Institut für Normung or DIN) as a universal paper size to replace the many formats in use.  It was adopted by DIN in 1922 (as DIN 476) and over the next 50 years many countries followed.  It was adopted as an international standard in 1975 (ISO 216).   Apart from North America (which still uses Letter (8½” x 11”) and Legal (8½” x 14”)), most other countries in the world now use the ISO 216 standard and the most commonly used paper size is A4.

ISO 216 defines the following requirements for A-series paper sizes:

  • Length divided by width = √2 (1.4142)
  • A0 size has area of 1 square metre (1m2)
  • Each subsequent size A (n) is defined as A (n-1) cut in half parallel to its shorter side.   For example, A4 is A3 cut in half parallel to its shorter side; A5 is A4 cut in half; and so on.
  • The standard length and width of each size is rounded to the nearest mm.
FORMAT DIMENSIONS(mm) AREA(m2)
A0 841 x 1189 1
A1 594 x 841 1/2
A2 420 x 594 1/4
A3 297 x 420 1/8
A4 210 x 297 1/16
A5 148 x 210 1/32
A6 105 x 148 1/64

 

Because each format has an aspect ratio of √2, it is simple to enlarge or reduce a document for printing on another ISO paper format.  Note also that you can place two A4 sheets side-by-side and they will equal an A3 sheet exactly;   and 2 sheets of A3 will equal an A2 sheet exactly; and so on. The basis for the whole system is the A0 format which has an area of exactly 1 square metre (1m2).  The significance of this will become clear when we discuss Paper Weights later.

The B-Sizes

The B-series was introduced to provide a wider range of paper sizes.  B paper sizes are larger than their A-series equivalents and are based on the geometric mean of two consecutive A-series sheets.  For example, B4 is between A3 and A4 in size and B5 is between A4 and A5.  The height-to-width ratio remains √2 in the B-series.

FORMAT DIMENSIONS(mm)
B0 1000 x 1414
B1 707 x 1000
B2 500 x 707
B3 353 x 500
B4 250 x 353
B5 176 x 250
B6 125 x 176

 

RA and SRA Untrimmed Sizes

These formats are used in commercial printing and are defined by ISO 217 (Paper – Untrimmed Sizes).  They are designed to allow for ink bleed during the printing process so that paper can then be trimmed to one of the A-series sizes.  RA stands for ‘Raw Format A’ and is 105% of the A-series size.  SRA stands for ‘Supplementary Raw Format A’ and is 115% of the A series size.  The aspect ratio is √2 as in the A-series.

FORMAT DIMENSIONS(mm)
RA0 860 x 1220
RA1 610 x 860
RA2 430 x 610
RA3 305 x 430
RA4 215 x 305
SRA0 900 x 1280
SRA1 640 x 900
SRA2 450 x 640
SRA3 320 x 450
SRA4 225 x 320

 

The C-Sizes

The C-series was introduced to provide an envelope with sufficient space for an A-series sheet.  An A4 sheet fits unfolded in a C4 envelope; an A4 sheet folded once fits in a C5 envelope; and so on.

FORMAT DIMENSIONS(mm)
C0 917 x 1297
C1 648 x 917
C2 458 x 648
C3 324 x 458
C4 229 x 324
C5 162 x 229
C6 114 x 162
DL 110 x 220

 

A very commonly used envelope – the DL – has been added to the above table.  While not strictly part of the C-series,   a DL envelope takes an A4 sheet folded twice (in thirds) or an A5 sheet folded in half lengthways.

Super A3 or A3+

This is not an ISO216 paper size but is occasionally specified.  Its dimensions are 329 mm x 483 mm and its aspect ratio is 1: 468 rather than 1: √2.

Paper Weights

We measure the weight of paper by defining its Grammage.  ISO 536 (Paper and Board- Determination of Grammage) defines Grammage as the weight in grams of one square metre ( units are written as gsm or g/m2) and this is in use throughout Europe and in most other parts of the world.  The US continues to use Basis weight which is the weight in pounds (lb) of a 500 sheet ream of uncut paper.

The weight of a single sheet of A0 paper defines the Grammage of that paper because as we have seen, ISO 216 defines the A0 size as having an area of exactly 1 m2.   Thus an A0 sheet of 80gsm paper weighs exactly 80 grams.  As an A4 sheet has an area of one sixteenth of 1 m2, an A4 sheet of 80 gsm paper weighs 80 divided by 16 = 5 grams.

 

 

 

 

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