Poster Print Resolution Calculator
Check the effective PPI of an image at a given print size and find the largest size it can print sharply — before you send it to a large-format printer.
How it works
Effective PPI = min(pixel width ÷ print width, pixel height ÷ print height) · Max size = pixels ÷ target PPI
Print sharpness depends on pixels per inch (PPI): the same file looks crisp small and blocky when blown up. Effective PPI is the pixel count divided by the print dimension, using whichever axis is more limiting. Required PPI falls with viewing distance — a photo held in hand wants ~300 ppi, a wall poster reads fine at ~150, and a billboard seen from far away can work at 100 or less.
Worked example
A 6000×4000 px photo printed at 24×16 in yields 6000 ÷ 24 = 250 ppi — good for a poster. To keep 150 ppi it could go as large as 6000 ÷ 150 = 40 in wide by 26.7 in tall.
Frequently asked questions
What PPI do I need for a poster?
Around 150 ppi is the sweet spot for posters viewed from a few feet away. Photo prints held close want ~300 ppi, while billboards seen from far off can drop to 100 ppi or less.
Can I just enlarge a small image?
Upscaling adds pixels but not real detail, so it only masks softness. It is always better to start from a higher-resolution original than to stretch a small file.
Why use the smaller of the two axes?
The image must cover the full print in both directions, so the limiting axis — the one with fewer pixels per inch — sets the real resolution you will see.
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This calculator is for educational purposes. Double-check important results before acting on them.