You can calculate the size, it depends on factors like the scale you set for the quads of the sections etc.
Let’s say if you choose a scale for the quads of 100.0 (=1 meter), I think you can multiply that with the overall resolution of the map.
You can find more info in the “landscape technical guide”: https://docs.unrealengine.com/latest…echnicalGuide/
You could also place an actor in the world, like a cube, and set its scale on the x-axis so it has a length of 1 km (or 1 mile in your case) so you can have a reference for a good view on the total size of your landscape while tweaking the parameters.