How can you find out how many blender units / meters / whatever units apart two points are?

For example, I’d like to plug in two objects locations and to get back a float saying how far apart they are (eg 3.816 units).

The obvious choice would seem to be the distance node. For some reason that I have trouble fathoming though, rather than return a simple number, this node returns… a four dimensional vector (!!!)

Alternately, is there a way to use nodes to convert this vector into a simple number representing the distance?