Here is some math.
1 gallon of propane generates 91600 btu's.
A 20 lb tank holds 4.73 gallons
Theoretically, the tank holds 433000 btu's but they usually only fill them 80%.
A medium sized BBQ rated for 40,000 btu's would last about 8 hours on high.
As suggested, check for the BTU rating of the gas range and do a quick calculation to get an idea.....and then take an extra tank!
Good luck.
you are correct. if it is a 4 burner stove like atwood or suburban. the burners will be 6000BTU each. if its a 3 burner the rear two are 6000BTU and the front centure is 9000BTU
im no good at math but i am a rv mechanic.