Resize Images for Printing (Free, with DPI table)

The 300 DPI rule

At 300 DPI a print looks sharp at arm's length. That means a 4×6 print needs 1200×1800 pixels and an 8×10 needs 2400×3000. Poster sizes viewed from farther away work at 150 DPI, halving the pixel count.

Common print sizes at 300 DPI

4×6 → 1200×1800. 5×7 → 1500×2100. 8×10 → 2400×3000. A4 → 2480×3508. A3 → 3508×4961. Use 10×15cm and letter (8.5×11) lists from your lab for exact numbers.

Resize to these pixel dimensions in the tool, then export as JPG at 90% — plenty of quality without a huge file.

Upscaling is the trap

Enlarging a small file to 300 DPI does not add real detail. If your source is 1200×1800, it is already a sharp 4×6 — print it as 4×6 rather than enlarging the same pixels to 8×10.

Pixels, DPI and actual print size

Print size is a division, not a setting: inches = pixels ÷ DPI. A 3000x2400 photo prints at 10x8 inches at 300 DPI, 15x12 at 200 DPI, or 30x24 at 100 DPI. Consumer photo labs work at 300 DPI, so a 6x4 print needs 1800x1200 pixels - smaller than most people assume, and upscaled 'enhanced' prints recover nothing that the sensor never captured.

Practical targets by output: 300 DPI for photo labs and fine art prints (glossy paper hides nothing, so quality matters most), 150-200 DPI for posters viewed at arm's length or farther - the eye cannot resolve the difference at that distance, and it saves enormous file size. Do not 'fix' a low-resolution file by upscaling it before print: labs print the pixels you send, and interpolated pixels are blurrier than native ones. Resize only downward to your lab's exact dimensions, keep color profile embedded if the lab asks for it, and send TIFF or maximum-quality JPG.