150 PPI or 300 PPI for a poster?

Viewing distance changes the useful resolution

A postcard is inspected at arm's length, while a trade-show panel may be viewed from several metres away. As viewing distance increases, individual pixels occupy a smaller part of the viewer's field of vision. That is why a large-format printer may accept a lower effective PPI than a photo lab producing a small fine-art print.

This does not mean every large file should be 72 PPI. A poster in a hallway may still be viewed closely. Begin with how the piece will actually be used, not just its physical dimensions.

Understand the file-size tradeoff

Doubling PPI doubles both pixel dimensions and creates four times as many pixels. A 24 × 36 in RGB poster at 150 PPI contains 19.4 megapixels; at 300 PPI it contains 77.8 megapixels. The higher-resolution version uses substantially more memory, takes longer to process and may exceed a printer's upload limit without producing a visible improvement at normal viewing distance.

Do not confuse upscaling with captured detail

Upscaling software can make edges smoother and reduce the appearance of pixelation, but it cannot recreate authentic texture with certainty. Inspect faces, type, logos and fine line work carefully. Vector logos and live type should remain vector whenever the production workflow permits it.

• Use the original camera or design export when possible.
• Keep text and logos vector in the layout application.
• Check sharpening at final output size, not at 400% zoom.
• Confirm maximum file dimensions with the print supplier.

Choose the lowest resolution that safely meets the job

For a close-viewed photographic poster, start near 240 PPI if the source supports it. For a general wall poster, 150–200 PPI is often a practical planning range. Use lower values only when viewing distance and the printer's workflow justify them. Always treat these as starting points rather than guarantees.