Most digital posters are either in the ratio 4:3 (standard size) or the ratio 16:9 (widescreen). The most common size for print posters is 48 inches wide by 36 inches tall.
A3 – 297 mm X 420 mm – 29.7cm x 42cm- 11.69nch x 15.52 inch – 1:1.41. A4 – 210 mm X 297 mm – 21cm x 29.7cm – 8.26 inch x 11.69 inh -1:1.41. A5 – 148mm X 210 mm – 14.8cm x 21cm – 5.82 inch x 8.26 inch – 1:1.41.
3:2 means the image is a multiple of 3 units wide, and a multiple of 2 units high. For example, 3” x 2” and 6” x 4” are both 3:2 ratio.
International paper size 'A3', portrait orientation, is 297 mm wide x 420 mm long (11.69″ x 16.54″); aspect ratio 1:1.414.
The measurements of A4 paper are 8.27 x 11.67 inches and they conserve the ratio between width and length of √2.
A3 – If you're looking for a little more room to play with, A3 can get your message across. It's commonly seen indoors in bars or shop windows – the right mix of detail and white space make it especially eye-catching. A2 – This is the perfect size for gig and event posters.
2:3 is the most popular aspect ratio for printing. Print sizes that are a 2:3 aspect ratio and are popular with poster, canvas, and decal printing are 24 x 36 inches and 40 x 60 inches. Some popular print sizes for the 3:4 ratio includes 30 x 40 inches and 18 x 24 inches.
An A3 piece of paper measures 297 × 420 mm or 11.7 × 16.5 inches.
A4 to A3 = 141% A5 to A4 = 141% From A3 to A1 = 200% A4 to A2 = 200%
The A2 format is 420 x 594 mm or 42 x 59.4 cm. In inches, A2 paper has a size of 16.5in x 23.4in. These dimensions mean A2 is normally the perfect choice for calendars, posters and larger format printing.
A2 is an appropriate and normal poster size for just about any project because it can be appreciated both close up and from a distance. This is also a regular poster size for framing, so you have many display options for A2.
Standard Paper Sizes
A3 has its shortest edge (297mm) doubled to be the longest edge of A2 (594mm). And similarly up to A0.
Is A1 a poster size? The A1 paper size is very slightly smaller than the standard large poster dimensions. Specifically, it is at 59.5 x 84.1 cm (23.4 x 33.1 inches), compared to the larger international poster size of 61 x 91 cm (24 x 35.8 inches) - which is the most common size for promotional and commercial posters.
18×24 is an appropriate and normal poster size for any project, as it can be enjoyed both up close and from a distance. This is also the regular poster size used for framing, so you have many options for displaying 18×24 posters.
The aspect ratio of A4 paper is 1:1.41, or 1:√2. The same is true for the entire ISO 216 standard that is used in most parts of the world. The reason for this choice is that it means every time the paper is halved, the resulting sheets retain the same aspect ratio.
16:9 Ratio
This international standard recently replaced the 4:3 ratio for monitors and TV screens, creating a slimmer, more elongated rectangular shape compared to the 4:3 format. Common resolutions in the 16:9 ratio are 1920×1080 pixels and 1280×720 pixels.
These numbers tell us how many evenly sized squares you can fit into a given rectangle. For example 2:3 means you can fit a grid of squares 2 high by 3 wide in the rectangle and 4:5 means you can fit 4 high by 5 wide.
Typical Poster Dimensions
Small Poster Size: A3 / 28 x 43 cm / 11 x 17 inches. Medium Poster Size: ~ A2 / 46 x 61 cm / 18 x 24 inches. Large Poster Size: Architectural D / 61 x 91 cm / 24 x 36. Movie Poster Size: either 68.6 x 101.6 cm / 27 x 40 inches or 101.6 x 152.4 cm / 40 x 60 inches.
So for instance an A4 sheet measures 210mm x 297mm making its shortest edge 210mm long. An A3 sheet measures 420mm x 297mm. so to move up a size 210 x 2 = 420. This gives an A3 sheet the flat size equivalent of exactly 2 A4 sheets.