* Trip odometer: Most vehicles have a trip odometer that can be reset to zero. When you fill up your tank, reset the trip odometer and start driving. When the trip odometer reaches the distance that is listed in your vehicle's owner's manual for the "fuel range," you should have about 1/8 of a tank of gas left.
* Fuel light: Most vehicles also have a fuel light that comes on when the fuel level is low. In general, the fuel light comes on when there are about 2 gallons of gas left in the tank. However, this number can vary depending on the make and model of your vehicle.
* Visual inspection: You can also try to visually inspect the fuel level in your tank. There should be a small window or indent on the side of your gas tank that allows you to see the fuel level. If you can't see any fuel, then your tank is probably empty.
It is important to note that these methods are not always accurate, so it is best to err on the side of caution and fill up your tank when the fuel gauge reaches 1/4 of a tank or less.
