Propane Tank Duration Calculator: Days & Hours

A propane tank's usable run time is a division problem: the energy the tank holds divided by how fast the appliance burns it. The one twist is that a tank is never filled to the brim — safety codes cap the fill at about 80% of water capacity so the liquid has room to expand as it warms. So a 100 gallon tank holds only about 80 usable gallons.

The tool takes that usable volume, multiplies by 91,502 BTU per gallon to get usable energy, then divides by the appliance's BTU-per-hour rating. The answer comes back in both hours and days so you can plan a refill before the tank runs dry mid-cold-snap.

Reality shortens the number. Appliances rarely run wide open around the clock — thermostats cycle them off — so a continuous-run figure is the shortest the tank could last. A furnace that runs half the time stretches a tank roughly twice as long as the raw estimate suggests.