At this gas station, tell the attendant that you need to fill full tank and go to the cashier. Wait until you pour the gasoline. The operator will call the final amount and the amount of gasoline that went into the tank.
If you don't know how much fuel may enter the fuel tank, refuel with a reserve. Arriving at the gas station, ask the operator to fill a full tank and leave the money with the stock. For example, you know that a full tank usually costs 1500P. So many leave. Insert the transfer hose into the tank and secure it in the middle. Once the tank is full, the fuel supply will turn off automatically. The scoreboard lights up, how many litres went in and the final cost. If gasoline came less than you paid, the cashier needs to refund you the difference.
If you want to calculate precisely how much fuel you need to refill to a full tank, you need to know the volume of the tank. For example, the volume of the tank you have 50 liters. To determine the exact amount of fuel remaining, you need to know the average fuel consumption. For example, the average fuel consumption of your car 10l/100km. After the fuel level sensor lit up, drive you twenty miles. This means that the tank is left with 2 litres of petrol. And to add you have 48 litres. These data may vary depending on the fuel consumption of each specific vehicle.