Pre-bake. Different dough formulas, management procedures, forming technique/method, types/styles will all influence the amount of bake shrink a pizza exhibits. If we measured the diameter post bake everybody would be using a different size pan, screen, disk or hand forming to a different size all to make the same size pizza in the end. When calculating thickness factor/dough loading again we use pre-bake diameter.
Tom Lehmann/The Dough Doctor