rule of thumb is put more gas in when its low, regardless of where your fuel pump is there is crap in your tank and it clogs up the filter and kills the pump.
i only needed this info because i used to do a LOT of highway driving (2 to 300 per day) and needed to know if i could make it to the next station.
and a oil change every month, i don't miss that job so much. although they did buy my gas and give me 5,000 a year to use my truck.