What is A3 size?

Twice A4, half of A2

Put two A4 pages next to each other along their long edges and the result is A3. Because the A series keeps the same proportions at every step, an A3 sheet can be folded to A4 and an A4 design can be enlarged to A3 without cropping or leaving empty bands. The inch figure is the one that confuses people in North America, where the nearest everyday size is the 11 by 17 inch tabloid or ledger sheet. The two are close, but A3 is about 18 millimetres wider and 12 millimetres shorter than tabloid, so a file made for one prints with thin gaps or slight cropping on the other. The pixel counts in the table simply multiply the inch dimensions by the density.

Where A3 is the right poster

Size should follow viewing distance and space. A3 works on noticeboards in schools, offices, libraries, clinics and shared kitchens, where readers stand within one or two metres and the board is covered in other notices. It also suits shop windows at eye level, doors, lift lobbies and counter stands. Moving up to A2 doubles the area, which helps when a poster must be read from across a room or compete in a large window, but on a crowded noticeboard A2 often overlaps its neighbours or gets folded to fit. A3 is also easy to print on demand, since many office machines take it, which matters for posters that change weekly, such as rosters, event schedules and menus.

Resolution and type size at A3

At 150 pixels per inch an A3 file is 1754 by 2480 pixels, and that is enough for a poster read from a metre away. The 300 DPI figure of 3508 by 4961 pixels matters for photographs that viewers can step close to, and for fine detail like maps. Type needs more attention than pixels. A headline that can be read from two metres on A3 needs to be roughly 60 points or larger, and body text should not drop much below 14 to 16 points. If a design was made for A0 and printed at A3, every letter shrinks to about a third of its height, which turns comfortable poster text into small print.

Common mistakes

The most frequent is starting from a screen sized image, such as a 1080 pixel social post, and printing it at A3, where it is roughly 65 pixels per inch and visibly soft. The second is using an A4 design's small text unchanged; enlargement helps a little, but a poster needs fewer words, not bigger paragraphs. The third is ignoring the printer's margins, since most office machines cannot print to the edge of an A3 sheet and will add a white border or scale the page down. The fourth is mixing up A3 and tabloid when sending files between countries. The last is shrinking a large research poster to A3 as a handout without checking that the smallest labels are still readable.

A3 and the poster and flyer builders

A3 is not a canvas size in either builder. Posters come in two sizes, A0 portrait at 1656 by 2340 pixels and A0 landscape at 2340 by 1656, and flyers offer A4 portrait, A4 landscape and six social sizes, with no custom size. Because every A size shares the same proportions, both routes still reach A3 cleanly. The A4 flyer export of 2480 by 3508 pixels printed at A3 lands at about 212 pixels per inch, and the A0 poster export of 3312 by 4680 printed at A3 lands at about 283, both above what a noticeboard needs. Choose by content: an A4 flyer design has type sized for a poster this small, while an A0 board shrinks to A3 as a handout. Exports are RGB with no bleed or crop marks, so ask the shop to scale to A3.

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