How much fuel is carried by aeroplanes ?

Many people know that there is more fuel in the tanks of an aeroplane
than what is needed for the actual flight.
But how much do you think is necessary? Check
Foz do Iguaçú - Caminhão tanque Volkswagen Worker 17-210 reabastecendo o Airbus A320 da TAM / Volkswagen Worker 17-210 tanker truck refueling the TAM Airlines Airbus A320