Poster size in pixels: what resolution do you actually need?

Published October 3, 2026

A poster is measured in inches or centimetres. Your image is measured in pixels. Turning one into the other takes one multiplication and one decision: how sharp you want the result.

The one formula

Pixels needed = size in inches × pixels per inch (PPI). A poster 18 inches wide and 24 inches tall, printed at 300 PPI, needs 18 × 300 = 5,400 pixels across and 24 × 300 = 7,200 pixels down.

The "DPI" number saved inside an image file is only a label. It adds no pixels and it doesn't make a print sharper. The pixel count is what matters.

Poster sizes in pixels

The table gives the pixels for common sizes at 300 PPI and at 150 PPI. The counts are for a portrait poster; swap width and height for landscape. A-series sizes are converted from millimetres (25.4 mm to the inch) and rounded to the nearest pixel.

Which pixels-per-inch number should you aim for?

There is no single answer, because three different people give you three different numbers. Follow the one that belongs to whoever prints your poster.

Our guideline: bigger posters are seen from further away

Osmanth Image judges a print by how far people usually stand from it. A small print is held or viewed up close, so it needs more pixels per inch. A large poster is viewed from further back, so it can get by with fewer. This is our own guideline, not a printer's requirement:

Printful: at least 300 DPI

Printful's file guidelines for its Enhanced Matte Paper Poster apply to every size from 5×7 in to 24×36 in. On the day we read them, they said:

Submit files in PNG or JPEG format with at least 300 DPI

If you order a Printful poster, that is the number to meet, not ours. At 300 PPI an 18×24 in poster needs 5,400 × 7,200 pixels, about 38.9 million pixels in total.

Printify: 300 is recommended, and it varies by product

Printify's help article says:

The recommended resolution for JPEG/PNG files is 300 DPI; however, a lower resolution file might also be sufficient (depending on the product).

It adds that the specific requirements differ for each product and are shown in Printify's product editor. When we opened that editor for Matte Vertical Posters on 27 September 2026, its print area was 3,600 × 5,400 pixels for 12×18 in, 5,400 × 7,200 for 18×24 in and 7,200 × 10,800 for 24×36 in. Each is exactly 300 PPI at that size.

What a real photo gives you

We ran two photos through the Osmanth Image check, one 3,000 × 4,000 pixels (12 megapixels) and one 4,000 × 6,000 pixels (24 megapixels). The table shows the pixels per inch each gives at a poster size, and how much of the picture the crop removes when the photo's shape doesn't match the poster's.

The first photo has the same shape as an 18×24 in poster, so nothing is cropped there, and the tool called it "Enough detail for this size." At 24×36 in it comes to 111 PPI. By our guideline that is above the lowest figure but short of the target, and the tool said: "Enough detail at normal viewing distance, but it won't be tack-sharp up close." The second photo has the shape of a 24×36 in poster and gives 167 PPI there, which the tool called "Plenty of detail for this size."

Against Printful's 300 DPI, though, neither photo is close at poster sizes. An 18×24 in poster at 300 PPI needs about 38.9 million pixels, and the first photo has 12 million. These numbers are what the tool reported for these two test photos; yours will differ.

Before you order

1. Find out who prints the poster, and use their number.
2. Work out the pixels with the formula, then compare with your image.
3. Don't try to fix a small image by adding pixels afterwards. It adds file size, not detail.
4. If you sell downloads rather than prints, the sizes work differently; see Etsy printable sizes.

The check runs on your device and your image is not uploaded; the privacy page explains exactly what that means.