To print a poster sharp, you need enough pixels for its size. The sum is the size in inches multiplied by the DPI. This page has the answer for every standard size so you don't have to do it.
If your size isn't here, the poster size pixel calculator works it out for any width and height, in inches, centimetres or millimetres.
Every poster size in pixels
300 DPI is the safe target. 150 DPI is fine for big posters that are viewed from across a room.
| Size | Inches | Pixels at 300 DPI | Pixels at 150 DPI |
|---|---|---|---|
| A5 | 5.83 x 8.27 | 1748 x 2480 | 874 x 1240 |
| A4 | 8.27 x 11.69 | 2480 x 3508 | 1240 x 1754 |
| A3 | 11.69 x 16.54 | 3508 x 4961 | 1754 x 2480 |
| A2 | 16.54 x 23.39 | 4961 x 7016 | 2480 x 3508 |
| A1 | 23.39 x 33.11 | 7016 x 9933 | 3508 x 4967 |
| A0 | 33.11 x 46.81 | 9933 x 14043 | 4967 x 7022 |
| 5x7 | 5 x 7 | 1500 x 2100 | 750 x 1050 |
| 8x10 | 8 x 10 | 2400 x 3000 | 1200 x 1500 |
| 11x14 | 11 x 14 | 3300 x 4200 | 1650 x 2100 |
| 12x18 | 12 x 18 | 3600 x 5400 | 1800 x 2700 |
| 16x20 | 16 x 20 | 4800 x 6000 | 2400 x 3000 |
| 16x24 | 16 x 24 | 4800 x 7200 | 2400 x 3600 |
| 18x24 | 18 x 24 | 5400 x 7200 | 2700 x 3600 |
| 20x30 | 20 x 30 | 6000 x 9000 | 3000 x 4500 |
| 24x32 | 24 x 32 | 7200 x 9600 | 3600 x 4800 |
| 24x36 | 24 x 36 | 7200 x 10800 | 3600 x 5400 |
| 30x40cm | 11.81 x 15.75 | 3543 x 4724 | 1772 x 2362 |
| 50x70cm | 19.69 x 27.56 | 5906 x 8268 | 2953 x 4134 |
| 12x12 | 12 x 12 | 3600 x 3600 | 1800 x 1800 |
| 20x20 | 20 x 20 | 6000 x 6000 | 3000 x 3000 |
One handy pattern: each A size at 150 DPI has the same pixels as the next size down at 300 DPI. A3 at 150 is A4 at 300. That is because each A size is exactly double the one below it.
How to work it out for any size
- Get the size in inches. For centimetres divide by 2.54, for millimetres divide by 25.4.
- Multiply each side by the DPI.
A 40 x 50 cm print at 300 DPI is 15.75 x 19.69 inches, which is 4724 x 5906 pixels.
Which DPI to use
- 300 DPI for anything people see up close: A5 to A3, 5x7 to 11x14, cards and small prints.
- 150 to 200 DPI for large posters, A2 and up, 18x24 and up. People stand further back, so they can't see the difference.
- Under 100 DPI looks soft at any size. Don't sell a size your file can only reach at this level.
The print resolution guide explains why viewing distance matters and why changing the DPI number in Photoshop adds no detail.
When your artwork is too small
Most AI art comes out far smaller than a poster needs. A typical 3:4 Midjourney image is about 928 x 1232 pixels. That's enough for a 3 x 4 inch print at 300 DPI, and nowhere near an 18x24.
You have three options:
- Upscale it before you do anything else. A 4x upscale takes that file to about 3712 x 4928, which covers 18x24 at around 200 DPI. Upscaling AI art for print compares the tools.
- Stop offering the sizes it can't carry. The print file checker shows the DPI of your actual file at every size.
- Make the file at the biggest size you sell, then let smaller orders scale down from it. Always make your poster file at the biggest size you sell explains why.
Pixels are half the job. Shape is the other half
Getting enough pixels doesn't help if your file is the wrong shape. A 3:4 file at 5400 x 7200 is perfect for 18x24, but it's the wrong shape for A2 or 16x20. The printer will crop it or add bars.
The print size fit checker shows which sizes your artwork fits as it is, and makes a bordered or cropped version for the rest. How to sell one poster in every print size covers when to crop and when to add a border.
The short version
- Pixels = inches x DPI.
- A4 at 300 DPI is 2480 x 3508. A3 is 3508 x 4961. 18x24 is 5400 x 7200.
- 300 DPI for small prints, 150 to 200 for big ones, never under 100.
- Check the shape as well as the pixels.
Frequently asked questions
How many pixels is A4 at 300 DPI?
2480 x 3508 pixels. A4 is 210 x 297 mm, which is 8.27 x 11.69 inches, and each inch needs 300 pixels. At 150 DPI it is 1240 x 1754.
How many pixels is A3 at 300 DPI?
3508 x 4961 pixels, about 17.4 megapixels. At 150 DPI it is 1754 x 2480, which is the same pixel size as A4 at 300 DPI.
How many pixels is 18x24 at 300 DPI?
5400 x 7200 pixels. Inch sizes are simple: multiply each side by the DPI. At 150 DPI, 18x24 is 2700 x 3600.
What size is a Midjourney image in print?
A typical 3:4 Midjourney image is about 928 x 1232 pixels. That is roughly 3 x 4 inches at 300 DPI, or 6 x 8 inches at 150 DPI. To sell it as a poster you need to upscale it, and to check the result at each size before you list it.
Is 150 DPI enough for a poster?
For large posters seen from a few feet away, yes. The eye cannot pick out the extra detail of 300 DPI at that distance. For anything held in the hand or hung at eye level close up, such as A5, A4 or 8x10, aim for 300.