well on my sportsman 500 ho i monitored the fuel bars as they went down heres how they went:
first bar 23 miles
second bar 4 miles
third bar 5 miles
fourth bar 4 miles
fifth bar 5 miles
sixth bar to low fuel 8 miles

these are approx integer values that are pretty close

BTW this is the first tank of fuel and it got about 50 miles to low fuel...