Fuel capacity is up to mom but fuel economy is up to each rider. If you search the forums you'll find that most people (a lot of which never had a fuel meter before their Vic) tend to fill up at intervals rather than trust a computer calculated guess.
I ride 10,000 plus miles per summer with a friend that rides a street glide. We both fill up at the same time at around 180 miles. Depending on how fast the 180 miles went we both put about 3.1 gallons in if we've averaged under 80 mph or 3.4 to 4.1 if we've averaged over 80 mph.
Results will vary depending on speed, weather, traffic, elevation, temp, etc...
Retired USAF, IYAAYAS!
2008 V-Star 1100 Custom Bobber project
2011 Crimson XR with Forged Highway Bars / Hard Bags / Passenger Backrest, Ness parts including Smooth Layback Plate Frame/Mount / Rad 3 Mirror / deep cut grips / drivers floorboards /shifter peg / brake peg / passenger pegs. Witchdoctor black rack, Lloydz filter / timing wheel / VFC III, 7Jurock windshield, Drag Specialties seat.