DPI, PPI and print size
Resolution describes how many dots or pixels fit into a length. DPI (dots per inch) is used for printers and scanners and PPI (pixels per inch) for screens and image files, but the conversion maths is identical. Metric equipment uses dots per centimeter: 300 dpi is about 118 dpcm.
To find how large an image prints, divide its pixel dimensions by the resolution. A 3,000 × 2,400 pixel photo at 300 dpi prints at 10 × 8 inches.
- 300 dpi: standard for photo-quality prints
- 150 dpi: acceptable for posters viewed from a distance
- 72–96 ppi: traditional screen resolution
Pixel pitch is the inverse measure: the distance between pixel centers. A 0.25 mm pitch is about 102 ppi.