How Long a Propane Tank Lasts
Updated October 2026
Whether you are running a grill, a patio heater, a generator, or a camp stove, the question is the same: how long will the tank last before it runs out? This calculator answers it from two numbers — the size of your propane tank and the BTU-per-hour rating of your appliance. The logic rests on a single physical constant: propane contains about 91,500 BTU of energy per gallon. Knowing how much energy you have and how fast you are burning it gives you the run time directly.
This matters most when you cannot afford to run out. Planning a long grill session for a party, sizing fuel for a power outage, or packing propane for a camping trip all depend on knowing the tank will outlast the need. The calculator also shows the run time at half output, since most appliances are not run flat-out the entire time — a grill on medium or a heater on a low setting lasts considerably longer than the maximum-burn figure suggests.
Propane tanks are named by the weight of propane they hold, which translates into gallons. The familiar grill tank is a 20-pound tank holding about 4.6 gallons; larger tanks scale up from there to 30-, 40-, and 100-pound sizes, and stationary home tanks are measured directly in gallons. One important detail: propane tanks are only filled to about 80% of their volume, leaving room for the liquid to expand safely as temperature rises. The gallon figures this calculator uses reflect usable propane, not the tank's theoretical maximum.
The calculation itself is simple multiplication and division. Multiply the usable gallons by 91,500 to get the total BTU available in the tank, then divide by your appliance's BTU-per-hour draw to get hours of run time. A full 20-pound grill tank holds about 4.6 × 91,500 ≈ 421,000 BTU; a 30,000-BTU grill burning at full output empties it in about 14 hours. If you are sizing a backup generator instead, the same math applies — just use the generator's fuel-consumption rating, and cross-check with the generator size calculator to make sure the unit itself is big enough.
The accuracy of the estimate depends on knowing your appliance's BTU-per-hour figure, which is usually printed on a label or in the manual. A typical gas grill runs 30,000 to 60,000 BTU per hour across all burners; a patio heater is often around 40,000; a small camp stove might be 10,000. Higher BTU means more heat but faster fuel consumption — there is no free lunch, and a powerful appliance simply trades run time for output. Because real-world use rarely holds maximum output continuously, treat the full-burn number as the conservative floor and the half-output figure as closer to typical use. For the electricity-cost equivalent of this kind of running-cost question, the electricity cost calculator handles powered appliances.
Use the half-output run time as your realistic estimate — few appliances run at full BTU continuously, so actual run time usually lands between the two figures.
Keep a spare tank on hand for grilling or heating. Running out mid-cook is the one failure the calculation is meant to prevent.
Remember the gallon figures are usable propane (about 80% of tank volume), so they already account for the expansion space.
For a generator, use its fuel-consumption rating rather than a heat output, and confirm the generator is sized for your load first.