Gallons or liters.
litres
You use litres to measure the capacity of a car's gas tank.
PPB
literes
The measure is cubic feet.
no
That depends what aspect of the gas you want to measure: its volume, its pressure, its temperature, its density, etc.
hundred cubic feet (Ccf)
Gallons.
litres
Liter
either replace the sending unit or the dash gauge, that is if there is electricity getting to the sending unit.