How is visual magnitude calculated (example)

[AK]

I've often read such a statement as "if you moved X object to Y location, it would have a magnitude of Z." Say, for example, if you moved Jupiter out to Uranus' orbit, its magnitude would be [whatever].

How is this figured? I assume there's some sort of equation that considers albedo, angular diameter etc. but I've never seen anything of the sort.

Thanks.

[QuagmaPhage]

I found this website which explains it in detail with equations.