Service manual says 18.8 liters, or 4.97 U.S. Gallons, or 4.14 imperial gallons.
Owner's manual (U.S.) apparently rounds up and says 19 liters, or 5.02 U.S. Gallons, or 4.18 imperial gallons.
Fuel light supposedly comes on at 4 liters remaining. The last time I had it come on, I filled it...