Introduction
DPI stands for Dots per inch and traditionally measures the number of ink droplets a printer produces per inch when printing an image on paper or other type of physical media. DPI is the resolution of a printer – the higher the DPI, the more detailed the print.
PPI stands for Pixels per inch meaning the number of image pixels printed per inch. Nowadays, the terms DPI and PPI are used interchangeably, and for the purpose of this article we will be using the DPI unit.
Rendered images are digital data and they have a size in pixels, not DPI. The size of a rendered image is called rendering resolution. It’s only when a rendered image is printed on physical media that its resolution can be measured in DPI.
How to set the DPI for printing?
Although rendered images can store a DPI value as metadata with some image formats like TIFF, it’s only indicative. The DPI value can be changed at any point with a number of software packages for image editing without changing the image size.
When rendering for print, it’s important to know the size of the area to print on. Based on that size, you can choose or determine the optimal DPI value.
| Size | 72 PPI/DPI | 96 PPI/DPI | 150 PPI/DPI | 300 PPI/DPI | 600 PPI/DPI | 720 PPI/DPI | 1200 PPI/DPI | 1440 PPI/DPI | 2400 PPI/DPI | 2880 PPI/DPI |
| 4A0 | 4768x6741 | 6357x8988 | 9933x14043 | 19866x28087 | 39732x56173 | 47678x67408 | 79464x112346 | 95357x134816 | 158928x224693 | 190714x269631 |
| 2A0 | 3370x4768 | 4494x6357 | 7022x9933 | 14043x19866 | 28087x39732 | 33704x47678 | 56173x79464 | 67408x95357 | 112346x158928 | 134816x190714 |
| A0 | 2384x3370 | 3179x4494 | 4967x7022 | 9933x14043 | 19866x28087 | 23839x33704 | 39732x56173 | 47678x67408 | 79464x112346 | 95357x134816 |
| A1 | 1684x2384 | 2245x3179 | 3508x4967 | 7016x9933 | 14032x19866 | 16838x23839 | 28063x39732 | 33676x47678 | 56126x79464 | 67352x95357 |
| A2 | 1191x1684 | 1587x2245 | 2480x3508 | 4961x7016 | 9921x14032 | 11905x16838 | 19842x28063 | 23810x33676 | 39684x56126 | 47621x67352 |
| A3 | 842x1191 | 1123x1587 | 1754x2480 | 3508x4961 | 7016x9921 | 8419x11905 | 14032x19842 | 16838x23810 | 28063x39684 | 33676x47621 |
| A4 | 595x842 | 794x1123 | 1240x1754 | 2480x3508 | 4961x7016 | 5953x8419 | 9922x14032 | 11906x16838 | 19843x28063 | 23812x33676 |
| A5 | 420x595 | 559x794 | 874x1240 | 1748x2480 | 3496x4961 | 4195x5953 | 6992x9922 | 8391x11906 | 13985x19843 | 16782x23812 |
| A6 | 298x420 | 397x559 | 620x874 | 1240x1748 | 2480x3496 | 2976x4195 | 4961x6992 | 5953x8391 | 9922x13985 | 11906x16782 |
Notes:
- This table shows the correlation of paper size, DPI, and resolution in pixels.
- The PPI describes image resolution in pixels per inch, however, in the context of modern printers and printing digital images, we can assume that PPI and DPI have the same meaning.
- The data in the table is taken from A4-size.
Lastly, the viewing distance to the printed copy can be an important factor when choosing the resolution to render at and the DPI to print at:
| Viewing Distance | Min Resolution |
| 0.6m/2ft | 300 dpi |
| 1m/3.3ft | 180 dpi |
| 1.5m/5ft | 120 dpi |
| 2m/6.5ft | 90 dpi |
| 3m/10ft | 60 dpi |
| 5m/16ft | 35 dpi |
| 10m/33ft | 35 dpi |
| 15m/50ft | 18 dpi |
| 50m/160ft | 12 dpi |
| 60m/200ft | 3 dpi |
| 200m/650ft | 1 dpi |
To better understand the application of DPI, change the DPI of an image without affecting its width and height. For example, render an image in 1920x1080px resolution and save it with 72 DPI, and then save it again with 300 DPI. The two files will be identical in terms of resolution, quality, and appearance. The DPI information stored in the files is taken into account only when importing them into a printing application or when you start printing. In such cases, the printer may interpret the two files differently, depending on the printer settings. For example, the file with the higher DPI may come out smaller, as the printer will attempt to print it with more pixels per inch, or the image may even become pixelated if you opt to fit the image to the printed paper size. This only depends on the printer settings and it is also possible to print the two files with exactly the same dimensions and exactly the same quality, regardless of their different DPI values. A 2D editor may also display the image with the higher DPI as a smaller image on the screen. However, the image can be scaled to your needs.
As the DPI value is just information for the printer, we suggest the following workflow:
- Use an online calculator to specify the ideal resolution of your rendered image. For example, to render a high-quality image in A5 format, you should use at least 300 DPI, which equals to 1748x2480px. The higher the image resolution in pixels you set, the better the image will look when printed in A5 format.
- Render your image and save it. You can specify the DPI at this point, e.g., in the Save as dialog of the TIF format, or later in a program such as Photoshop without changing the resolution. You can even use the standard "monitor" DPI value of 72.
- When printing your image, make sure in the printer software that your image covers the intended area on paper (in this example - A5). We already made sure that the image resolution is high enough for A5 print, so the quality of the print will be good.
Note: When using external services for printing, they may ask you for an image with a specific DPI value. In that case, you can specify the required DPI value when saving your file or by resaving your file in a 2D editor, but regardless of the DPI value specified in the file, it is always a good idea to additionally inform the printers about the physical dimensions of the image you are sending to them (for example A5, 148 x 210mm, 5.8 x 8.3in).