Free tool — runs in your browser, no sign-up
Aspect Ratio Calculator for Print & Posters
Enter dimensions to get the simplified ratio, or enter a ratio and one side to solve for the other. Presets are print and poster ratios — not social-media crops.
How it works
Choose your starting point
Have exact dimensions, or a ratio and one known side — either works.
Enter your numbers
Any unit works for dimensions since the ratio is scale-invariant.
Read the result
Get the simplified ratio, the matching print-size preset, and the missing side.
Standard print & poster ratios
The ratios most art and print sellers actually need — not the 16:9 / 9:16 video and social presets every generic ratio tool defaults to.
| Ratio | Use | Example sizes |
|---|---|---|
| 1:1 | Square | 12x12, 20x20 |
| 4:5 | Portrait poster | 8x10, 16x20 |
| 3:4 | Classic framed print | 9x12, 18x24 |
| 2:3 | Most common poster | 12x18, 24x36 |
| 5:7 | Photo print | 5x7, 10x14 |
| 11:14 | Half-sheet / lobby poster | 11x14, 22x28 |
| 1:1.41 (√2) | ISO A-series | A4, A3, A2, A1 |
Frequently asked questions
What is the most common aspect ratio for posters?▾
2:3 is the most common print-poster ratio — it covers sizes like 12×18 and 24×36. 3:4 (18×24, 9×12) and 4:5 (8×10, 16×20) are the next most common. Enter your dimensions above to see which standard ratio yours matches.
What aspect ratio is 24x36?▾
24×36 simplifies to 2:3 — the same ratio as 12×18, 16×24, and 20×30.
What aspect ratio is 8x10?▾
8×10 simplifies to 4:5 — the same ratio as 16×20 and 4×5 photo prints.
How do I find the height for a given width and ratio?▾
Switch to "Ratio & one side" above, enter your ratio (e.g. 2:3), select "Width" as the known side, and enter your width. The calculator solves for the height automatically.
Is A4 the same ratio as US letter?▾
No. A4 (210×297mm) uses the ISO A-series ratio of 1:√2 (≈1:1.414). US letter (8.5×11in) is a slightly different ratio, close to 17:22. They look similar but are not interchangeable without cropping or white space.
Does changing DPI change the aspect ratio?▾
No — DPI only affects pixel dimensions and print sharpness, not proportions. If you need to check whether your image file has enough resolution for a print size, use the print resolution checker instead.
Related tools
Right ratio? See it on the wall.
Preview your art at true scale in a real room scene — free for 7 days.
Try WallMockup free