My mileage varies depending on the route and how many errands I run (stop and go), so I end up with another method for checking the fuel level.
Sitting on the bike, engine off, tip it from right to left (or left to right) and the gas will slosh in the tank. Not much slosh noise, and easy tipping back and forth means it may be time to fill up.
The tank feels heavier when it is full (duh) and is harder to tip. But I can now tell by the weight when it is half full or not as low, which is very handy (another day of passing the gas station without filling up!)