I can remember this subject being discussed a while back. I was reading one of my Mag's "Practical Boat Owner" and come across this equation that may be of some help to many.
Using a Plastimo
Neptune hotplate burner as the subject.
Hotplae = 1.65KW
If you used all burners for one hr a day, the sum would be
Total = 4.63KW
Both Butane and Propane
produce 14KW of energy per 1KG of gas.
So 4.63 over 14 =0.33Kg per day.
X 30 days = 9.9Kg gas per month.
Hopefully there are enough figures in there so as anyone can work any calculation they want.