When defining layout in a UWP app, measurements are in effective pixels (EP).
Here, for my reference as much as yours, is how the EP values for a range of devices compare.
|55" Surface Hub||1920x1080|
|84" Surface Hub||2560x1440|
Or to compare they can be visualized like this:
There's also HoloLens and IoT devices to potentially consider too.
Details for HoloLens are not yet available and the range of possible screens you could connect to an IOT device is incredibly broad so I chosen to leave it out.