I'm not positive exactly how much it holds total but what I do know is that when mine and most my friends bikes low fuel kicks on if topped off immediately it takes 3.2 gallons to top it off.
Do this a few times, calculate your mileage, and figure out from someone who knows exactly how much an empty tank holds and you should be able to answer your question.
I went 160 miles once with running out but I was riding about 50 and very very modestly, and had a spare 1 gallon can with me at the time to cover my ass.
My low fuel light used to come on at 110-120 miles, with the new engine I don't know where it's at but probably gonna be about 80 miles if I'm lucky.