What is A1 size?

Half of A0, four A3 sheets

In the ISO system A0 is one square metre and every smaller size halves the one above, so A1 is half a square metre. Two A1 sheets placed side by side make A0, and one A1 holds four A3 or eight A4 pages. The same one to root two ratio runs through every size, which means an A0 design reduces to A1 without distortion, with every element at about 71 percent of its original width and height. The North American 24 by 36 inch poster is the size most often confused with A1. It is slightly larger in area and noticeably longer in proportion, 1.5 against 1.414, so the same artwork will not fill both without cropping or leaving a strip empty.

When a conference or venue asks for A1

Poster sessions set their size by the boards they hire. Larger international meetings mostly specify A0, while regional meetings, hospital research days, university showcases, student conferences and trade exhibitions often ask for A1 because more posters fit in the same room. Architects and engineers use A1 for drawing sheets, and galleries and shops use it for display prints. Always read the organiser's instructions, which usually state a maximum width and height and an orientation. A board rated for A0 will display an A1 poster, but it looks undersized next to its neighbours; an A0 poster on an A1 board simply will not fit, so bringing the larger size by mistake is the costlier error.

Designing for A1 rather than shrinking A0

A1 is read from about the same distance as A0, a metre or two, but it has half the area. That means content has to be cut, not shrunk. A poster designed for A0 with body text at 24 points drops to about 17 points at A1, which is still readable up close but tiring from a step back, and figure labels that were already small become hard to read. The better approach is to keep the type sizes an A0 poster would use and remove material: one fewer figure, a shorter method, fewer references. In pixels, A1 at 150 pixels per inch is 3508 by 4967, and at 100 it is 2339 by 3311, which is enough for a board read from a metre.

Common mistakes

The most common is confusing A1 with 24 by 36 inches when printing across countries, then discovering a strip of white or a cropped footer at the venue. The second is reducing an A0 board to A1 without checking the smallest text, which is usually the axis labels, table cells and references. The third is using a portrait poster when the organiser's boards are landscape, or the reverse. The fourth is packing the extra space of a nearly empty A1 with decoration rather than white space. The fifth is ordering the print too late; large format printing often takes several days, and university print services get busy in the weeks before a conference season.

A1 and the poster builder

The poster builder offers two sizes, A0 portrait at 1656 by 2340 pixels and A0 landscape at 2340 by 1656, with 20 templates for each orientation. There is no A1 canvas and no custom size. Because A1 is exactly half of A0 in the same proportions, an A0 board can be printed at A1 with no cropping. The A0 export is 3312 by 4680 pixels, which at A1 lands at about 141 pixels per inch, more than a poster viewed from a metre needs. The limit is type, not resolution: plan for text at 71 percent of its A0 size and cut content before exporting if the board is dense. Exports are RGB PDF, PNG or JPG with no bleed or crop marks, so ask the print shop to scale to A1 and confirm the orientation.

Questions people ask