A photographic print is created by laying a number of colored dots onto paper. The larger the surface, the more these dots have to be spread apart to fill the surface. At a certain point, the photograph will start to look grainy and less apealing. Some printing processes need more dots per square inch to produce a quality image. Magazine editors often require 300 DPI or more, while digital photography labs usually recommend a minimum print resolution around 212 DPI or more for their process.

Using an example of 212 DPI, you can get the maximum print size by dividing the file's resolution (in pixels) by 212. If an image file is 2560 pixels wide by 1920 pixels high, the print size at 212 DPI would be 12" x 9" (2560 / 212 = 12 and 1920 / 212 = 9).