Approximately 1.5 gallons.... I'm guessing your fuel gauge is optimistic & has not had the usual "fix" applied to it yet?
Fix#1; remove seat, remove tank, remove sending unit, bend float arm, re-assemble, fill with gas, ride until you need to flip on reserve, see if fuel gauge reads correctly, if it does, great, if not repeat procedure all over again.....
Fix#2; go to your favorite electrical hooby shop & pick up a 1/4 watt 250 ohm resisitor... remove seat, locate electrical connector for sending unit, use the resistor to jump the two wires from the sending unit at the connector, seal it up with electrical tape, re-assemble & you're good to go.....you'll find that the bike will need to switch to reserve when the fuel gauge nears the halfway mark in the red zone....
Good Luck