DPI (or dpi) stands for dots per inch and is a measure of the spatial point density, mostly used by printers. It indicates how many individual points can be placed in a 2.54 cm (1 inch) line.

The color points are directly dependent on the number of color sources of the devices used. A simple inkjet printer delivers 4-6 colors (known as ink cartridges). The color points can change in size and thus influence the color character and the color intensity.

Misunderstanding and misnomer DPI or PPI

Today, DPI has established itself as a quasi synonym for PPI in photography and scanning, although the term DPI is strictly incorrect in these areas. Even technical reports and device or camera documentation almost only speak of DPI when it comes to image resolution, but correctly it is always about PPI.

DPI properties

  • Different point size
  • Reduced number of basic colors per point (e.g. 4 -6 colors for printers)
  • Pixel colors have to be created by several DPI points
  • A 1200 dpi printer with a 6x6 matrix can only display one 200 PPI pixel

DPI is mostly only used for printers that have to get by with a few basic colors per point:

  • Laser printer
  • Inkjet printer

Colors can only be represented by mixing the basic colors and the size of the dots. With a good print, the human eye cannot see the dots, only with a close-up like in the following picture they become clear:

DPI calculation

To calculate DPI, you need the number of points over a certain length. If it is a metric (mm, cm) length, it must first be converted into inches. Use the following formula or our DPI calculator:

\(DPI = {Dots \over Length (Inch)} = {dots \over in} = {dots * 25.4mm \over mm} \)

\(DPI = {Dots \over Length (Inch)} = {20 dots \over 0.12 in} = 172 DPI \)

Difference between PPI and DPI

Digital recording and display devices such as cameras, projectors and monitors do not have points but pixels, the dimensions of which are PPI (pixels per inch). Many resources use the terms DPI and PPI synonymously due to the minimal difference. Both measures are calculated exactly the same. In order to be able to tell the terms apart, another picture that illustrates the difference: