How to find out your car's mileage

Immensely, uncharacteristically practical, I know. Clearly the best way to undertake this is to run your car to empty.
Do not try this when your driveway runs at a forty-five degree incline and you habitually park at the bottom of said incline.
The really stupid part of my little adventure is that I have actually done this before. The resulting sheepish phonecall was made: "Sweetheart, my car won't start... on your way home tonight could you stop and get me some petrol?"
Him: "Where are you? Call the RACV!"
Me: "Ah, noooo, it's definitely a petrol issue. I'm in the driveway."
Hmmm. So today after hopping out and debating with myself if I could possibly push my baby up the drive solo, I had one last try. Oh, the sound of a revving motor has never been so sweet! First stop: petrol station.