What is the difference between PPI and DPI?

PPI describes the file's image points per inch (image resolution), DPI the printer's ink dots per inch (printing technology). Print size depends on PPI.

Which figure do I need for print size?

PPI. The maximum print size is the pixel count divided by the desired PPI resolution.

PPI vs DPI

Category: Print

PPI (pixels per inch) is the file's image resolution, DPI (dots per inch) the printer's dot density. The two are often confused but must be kept clearly apart.

PPI and DPI sound similar but describe different things. PPI – pixels per inch denotes how many image points of the digital file fall on one inch of output surface. This is the correct measure for describing the detail resolution of an image at a given print size.

DPI – dots per inch, by contrast, denotes how many ink dots the printer physically places per inch. Printers often use several ink dots for a single image point, which is why a printer's DPI figure is regularly higher than the meaningful PPI resolution of the image.

For calculating the maximum print size of a gigapixel image, PPI alone is decisive – not the printer's DPI figure.

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Explained by Daniel Richter · Expert in gigapixel photography · Gigapixel GmbH

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