Font vendors should create one set of screen fonts for each of the popular aspect-ratio classes for displays. The aspect-ratio classes determine the relative shape of pixels on the device, and therefore affect the design and implementation of screen fonts. Windows recognizes two major aspect-ratio classes.
| Class | Typical device |
| 1.33:1 (4:3) | The IBM Enhanced Graphics Adapter |
| 1:1 | The IBM PS/2 MCGA, VGA, and 8514/a |
The actual dots-per-inch resolution is not a factor in determining the class of the device; only the aspect ratio is used.