Blender Cycles A correct sun size

I ve attempted to come up with a value for the sun size in Blender Cycles that would correspond to the real world sun size to produce shadows in Blender that have a realistically sized penumbra. I came to the conclusion of 0. 005 blender units (or 5mm if you have metric units on) on the sun size being much closer to the real world than the default 0. 1. Do these measurements all make sense or am I not thinking about something It d be awesome if someone who knows more about these things could ch