All QScreen functions return screen geometries with scaled values, which is good for most cases. However, sometimes there is a need to communicate with external applications with device pixel sizes.

It is not possible to calculate because there will be rounding errors. For example, resolution of 3200x1800 will cause problems with 1.5 and 3 scale factors because:

3200x1800 / 1.5 = 2133x1200
2133x1200 * 1.5 = 3199.5x1800

and:

3200x1800 / 3 = 1066x600
1066x600 * 3 = 3198x1800