Paste a list of places. Get the distance from every one to every other, in a grid. Free, no signup.
Either. Choose driving distance or drive time for numbers on real roads (normal traffic, not live), or straight line for as-the-crow-flies distance, the usual choice for territory work and site shortlists.
12 places is 66 pairs, which keeps the grid readable. Need more? The InstaMaps add-on computes distances for whole spreadsheet columns.