Paper sheet and envelope sizes

Over time, there have been many conventions of paper sizing. The present-day standards date back to 1975, when the ISO standards regarding paper sizes were issued.

The most popular A-series sizes are based on the findings of Georg Christoph Lichtenberg, a German scientist, who noticed that a rectangle with the √2 side ratio has some unique scaling properties. The basic format, A0, was designed to have the area of 1m2. A1 was achieved by folding the A0 sheet in half across the longer side, A2 is a result of folding A1 in half etc. Each of the subsequent sheets obtained this way has the aspect ratio of √2, too.

A-series paper sizes (especially A4) are common for office use.

ISO 216 paper size, A series	Measurements [mm]
A0	841 x 1189
A1	594 x 841
A2	420 x 594
A3	297 x 420
A4	210 x 297
A5	148 x 210
A6	105 x 148
A7	74 x 105
A8	52 x 74
A9	37 x 52
A10	26 x 37

The less popular B-series was designed to be an in-between size for the A-series. For example, B1 is a size between A0 and A1. B-series are used for, e.g., passports and printing press.

ISO 216 paper size, B series	Measurements [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
B7	88 x 125
B8	62 x 88
B9	44 x 62
B10	31 x 44

C-series (plus and additional format called DL) are used for sizing envelopes:

C-series; envelope sizes	Measurements [mm]
DL	110 x 220
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
C7	81 x 114
C8	57 x 81
C9	40 x 57
C10	28 x 40

Did you know?

The envelope sizes were designed in such a way that they go well with A- and B-series papers. Taking the most common A4 paper size as an example:

- C4 envelope can fit unfolded A4 sheet of paper
- C5 envelope can fit A4 sheet folded in half
- C6 envelope can fit A4 sheet folded twice (¼ A4 sheet size)
- DL envelope can fit 1/3 A4 sheet