I fill up some where between 1/8 and a 1/4 tank, just replaced my fuel pump last November, but it was giving me proplems before that.
That means my fuel pump lasted 6 years....

If I were to lose my fuel gauge and had to use the odometer when I needed to fuel up it would depened on the driving. i.e. was it city or hwy or both.
300km combine, 400km hwy and 200km city.
I may have lots of fuel left in the tank, but I wouldn't run out!