average fuel consumption?

Hi,
as with a lot of things it depends on your speed, altittude, winds.  for me flying at 34,000ft at 480ish kts i get about 500 ish gallons an hour.  you  should always put in more then enough for me about 1000 gallons more then I need depending on which internatiinal airport I am going to as I know say for example Heathrow I know I will need to go around at least once.

for fuel planing what i do and it always works is select the plane first, then make the flight plane and look at the nav log page in the flight planing bit and that tells me how much to put in. I hope this helps.