1994 Subaru Impreza gas gauge

You have about 12 gallons of usable gas in the tank, and your average mpg is about 25. If you multiply 12 x 25 = 300.

Fill up your tank all the way to the top. Reset your trip odometer to zero. If you don't have a lead right foot, you should be able to drive about 300 miles before fueling up. Always refuel at 250 miles and you won't have to worry about running out gas. Reset the trip odometer every time you refuel and don't go past 250 miles every full tank. I did that for two years until I finally replaced the faulty sending unit.

***Your car's actual figures and averages maybe slightly different than the example, you need to adjust the formula accordingly.***