Propane Tank Duration Calculator
See how long a propane tank lasts running an appliance at a given rate.
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.
usable fuel = 100 × 0.80 = `80 gal` (about `303 L`)
run time = (80 × 91,502) ÷ 30,000 = `244` hours ≈ `10.2` days