Standard Poster Sizes in Inches, cm and Pixels

Poster sizes look simple until you try to make a file for one. A 24x36 poster isn’t the same shape as your photo, the print shop wants a certain number of pixels, and most “standard poster size” lists stop at inches. This page lists every common poster size in inches, centimetres and pixels, says what DPI a poster really needs, and checks which phone photos are big enough.

Quick answer: The standard US poster sizes are 11 x 17, 12 x 18, 18 x 24, 24 x 36 and 36 x 48 inches, with 27 x 40 for movie posters and 22 x 28 for poster board. The A series runs A3 to A0. At 150 DPI, which is fine for a wall, 18 x 24 needs 2700 x 3600 pixels and 24 x 36 needs 3600 x 5400.

Standard poster sizes in inches, cm and pixels

The pixel numbers come from one formula, pixels = inches x DPI. If you want the long version, with the 72 DPI myth and the metric conversion, it’s in image size for printing. Here are the results, portrait. Swap the numbers for landscape.

These are the sizes printers actually sell. Staples prints same-day posters at 12 x 18, 16 x 20, 18 x 24 and 24 x 36. FedEx Office lists 16 x 20, 18 x 24, 22 x 28, 24 x 36 and 36 x 48. Mpix sells poster prints at 12 x 18, 16 x 24, 20 x 30, 24 x 36 and 36 x 48, with a 1/8 inch white border on every side, so leave a little room at the edges for that one.

Two rows need a note. Poster board is the 22 x 28 inch sheet sold in packs at Staples and Office Depot, the one used for school projects. And 27 x 40 is the US theatrical one-sheet. Frame shops sell 27 x 40 frames for exactly that, so if you’re printing a film poster to fit one, use 27 x 40, not 24 x 36.

A-series poster sizes: A3, A2, A1 and A0

Outside North America, posters follow ISO 216 paper sizes. A0 has an area of one square metre, 841 x 1189 mm, and each smaller size is the one above cut in half, as DIN explains in its history of the format. Every A size has the same shape, about 1:1.41.

A3 is close to 11 x 17 but not the same. It’s a little wider and shorter, so a file made for one gets cropped or shows white edges on the other.

What DPI a poster really needs

300 DPI is the number everyone repeats, and it’s right for a photo in your hand. A poster is different, because nobody reads it from 30 cm away. Vistaprint’s poster preparation guide sets it by viewing distance: 300 DPI for posters seen up close, 240 for most indoor posters, 200 for larger ones, and 150 for big prints viewed from across a room.

The labs’ own minimums tell the same story. Walgreens’ image requirements ask for 5400 x 3600 pixels for a 24 x 36 poster, which is exactly 150 DPI. Mpix says in its photo prep help that its printers output at 250 pixels per inch, a little under the 300 everyone quotes. Its table puts a 20 x 30 at 5000 x 7500 pixels as optimal and 2000 x 3000 as the minimum.

So my rule: 300 DPI if you have the pixels and the poster has small text, 150 DPI for a photo on a wall. Some shops, Staples among them, still ask for 300 DPI files, so check the order page before you upload.

Is a phone photo big enough for a poster?

A 12 MP phone photo is about 4000 x 3000 pixels. Recent iPhones save 24 MP by default and can shoot 48 MP if you turn on Resolution Control in camera settings. A 24 MP photo is roughly 5700 x 4300 pixels. Here’s how far each one goes at 150 DPI:

18 x 24 is the sweet spot for phone photos. It’s 3:4, the same shape most phone cameras use, so nothing gets cut. 24 x 36 and 12 x 18 are 2:3, which cuts about 11% off the width of a portrait 4:3 photo. The 11 x 17 cuts about 14%, and the A sizes about 6%.

Falling short doesn’t mean you can’t print. A 12 MP photo on a 24 x 36 poster looks fine from a few steps back and a bit soft up close. What doesn’t help is upscaling it first. You’ll get the right pixel count, but enlarging can’t add detail the camera never captured.

How to resize a photo for a poster in ResizeAny

ResizeAny runs in your browser, so the photo stays on your device.

1. Open the size you need: 11x17 inch, 12x18, 18x24 inch, 24x36 poster, A3 or A2. For A1 and A0, type the size in mm.
2. Set the DPI field. The 18x24 page fills in 300. On the others, type 150 or 300 yourself, because with DPI on Auto the tool converts inches at 96 DPI and a 24 x 36 comes out at only 2304 x 3456 pixels.
3. Under Ratio & fit, pick Crop to fill the poster and trim the edges from the centre. If you’d rather choose what gets cut, use the Crop tool first: it has 3:4 for 18 x 24 and 36 x 48, and 2:3 for 12 x 18 and 24 x 36. Use freeform for the rest. Leave it on Stretch and the photo gets squashed to fit.
4. Download as JPG. The DPI goes into the file, so the print shop reads the right size.

There’s one hard limit. Everything happens in the browser, so ResizeAny caps output at about 120 megapixels. 36 x 48 and A0 at 300 DPI go over it. Use 150 DPI for those, which is the sensible number at that size anyway.

Making a set of matching posters? Bulk image resize handles up to 100 photos at once with the same size and DPI. Every other print and paper size we have is in the print, paper and photo presets.