Cessna 152 6 gallons/hr
People I usually hire from require the sums to be done at 7 gallons/hr (USG, that is) (the book says around 5.5).
I check the log, and then check the fuel gauges (which aren't that bad), and then dip the tanks, and I refuel before departure if all three data sources don't agree that there is enough for the flying time + taxi and takeoff as per POH + 1 hour reserve (which is more than plenty given there's a runway every few minutes round here).
Then I check the gauges every few minutes during the flight, and would land if I saw anything unexpected. Hasn't happened. Yet.