What is A2 size?

The halving rule, explained once

The whole A series starts from one sheet. A0 has an area of one square metre and a ratio between its sides of one to the square root of two, about 1 to 1.414. Cut A0 in half across its long side and each piece is A1; cut A1 in half and each piece is A2, and so on down the series. The square root of two is the only ratio that survives this cutting, which is why every A size has exactly the same shape. The Cambridge notes on ISO paper formats describe the practical result: a document can be enlarged or reduced between sizes with no cropping and no empty margins. A2 is two steps below A0, so it has a quarter of the area and half the width and height.

Where A2 works

Poster size should match the distance it will be read from and the space available. A2 is comfortable in a shop window viewed from the footpath, on a wall in a corridor or waiting room, on a cafe door, at a trade stand as a secondary poster and in standard ready made frames. Paper size references commonly list wall charts and display posters as its typical uses. It is large enough that a bold headline can be read from several metres and a single strong image carries, yet small enough to carry under an arm, post in a tube and print on the wide format machines found in most print shops. When a poster must be read from across a hall, or holds a full scientific study, A1 or A0 is the better size.

Resolution at A2

In pixels, A2 at 150 pixels per inch is 2480 by 3508, which happens to be the same pixel count as A4 at 300 DPI. At 300 DPI it is 4961 by 7016 pixels, a large file that only close up photographic prints need. A window or wall poster viewed from two metres or more looks sharp at 150, and often at 100, which is 1654 by 2339 pixels. Photographs are the limit. An image that fills half the poster needs roughly half those pixels along each side to avoid looking soft, so a small phone crop or a picture copied from a website will show its pixels at this size even when the text is crisp.

Common mistakes

The first is assuming an A4 design will read at A2 simply because it is bigger. Everything grows by the same factor, but the viewing distance grows more, so small print that worked in the hand is still too small from across a shop. Posters need fewer, larger words. The second is supplying a file at a different shape, such as 18 by 24 inches, and expecting it to fill A2; the ratios differ, so the shop has to crop or pad. The third is forgetting frame rebates: a frame's lip covers several millimetres of each edge, so keep text well inside. The fourth is sending a heavily compressed JPG, whose blocky artefacts are hidden on screen and obvious on a large print.

A2 and the poster and flyer builders

A2 is not a canvas size in either builder, and there is no custom size. Posters are A0 portrait at 1656 by 2340 pixels or A0 landscape at 2340 by 1656, and flyers offer A4 portrait, A4 landscape and six social sizes. The halving rule is what makes that workable. An A0 poster export of 3312 by 4680 pixels printed at A2 lands at about 200 pixels per inch, and an A4 flyer export of 2480 by 3508 printed at A2 lands at 150, both enough for a poster on a wall. A window poster with one headline and one photograph is usually better started as an A4 flyer design, since flyer layouts carry fewer, larger elements. Exports are RGB PDF, PNG or JPG without bleed or crop marks, so tell the print shop to scale to A2.

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