Every page that answers this gives you a number of hours. Almost none of them tells you which fire pit that number is for, which is the only thing that determines the answer.
The arithmetic is genuinely simple, the inputs are printed on two things you already own, and doing it yourself takes about two minutes. That is what this page is for.
Before the arithmetic: the propane safety line
Propane is a fuel gas and the rules around it are not decoration.
Store the tank outdoors, upright, in a ventilated place. Never in a basement, never in a closed garage, never indoors. Propane is heavier than air and pools in low spaces.
Never bring a connected tank inside. Never use a fire pit indoors or in an enclosed or partially enclosed space, whatever the fuel.
Check connections with soapy water, not a flame. If you smell gas, shut the valve at the tank, move away, and do not operate anything electrical.
Do not modify the regulator, the hose or the burner. Gas appliance modification is not a homeowner job, and a regulator is a safety device rather than a restriction.
Transport and refill according to the supplier's instructions, and observe the fill limits they work to. Overfilled tanks vent, and a venting tank is a hazard rather than a nuisance.
If any of the fittings on your pit look damaged or the hose is cracked, replace them with the manufacturer's parts or have the appliance looked at. That is where this article stops and a gas professional starts.
The arithmetic
Two numbers, both of which you can look up in a minute.
Number one: your fire pit's BTU rating per hour, at full output. It is on the rating plate or in the manual. This is the number that varies enormously between products, which is why a single published "hours" figure cannot be right for everybody. Two pits sold beside each other can differ by a factor of two or more.
Number two: the energy content of the tank. A standard 20 lb barbecue cylinder holds about 20 pounds of propane when filled to the normal limit, and propane's energy content per pound is a published physical constant that your supplier or the tank literature will state. Multiply the two and you have the total energy in a full tank.
Then divide. Total tank energy, divided by your pit's BTU per hour, gives you hours at full output.
That is the whole calculation. We are deliberately not doing it for you with numbers, because the result would be a figure for a fire pit that is not yours, printed as though it were general, which is the exact failure this page exists to fix. Your two numbers are on your rating plate and your tank.
Five things that make the real answer shorter than the calculation
The number you get is a ceiling. Real life is below it, for reasons that are all predictable.
You are unlikely to run at full output. Most people turn the flame down after the first ten minutes. Running at half output roughly doubles the hours, which is the single largest variable.
Cold weather reduces vaporization. Propane has to boil off inside the tank to become gas, and that draws heat from the tank. In cold conditions, and especially with a nearly empty tank, the pressure drops and the flame weakens. You will notice this as a fire pit that gets feeble on the coldest evening of the year, which is the evening you wanted it most.
A tank is rarely full when you buy it, and exchange tanks are often filled below the maximum. An exchange cylinder can hold noticeably less than a tank you have refilled by weight at a filling station, which is a real difference in cost per hour and one of the few genuinely useful things to know in this category.
Wind costs you gas. Not because the fire burns faster, but because you turn it up to compensate.
The last portion of a tank underperforms as pressure falls. Plan to have a second tank rather than to run one to nothing.
What this means for buying
If you are choosing between pits, the BTU rating is a running-cost decision as much as a heat decision. A pit with double the rating gives you a bigger flame and halves your hours per tank at full output.
Bigger is not automatically better here. A modest rating run at full output often looks better and lasts longer than a large one run low, and low output on a large burner can produce a lazier flame.
And if you find yourself doing this arithmetic and disliking the answer, that is a signal worth taking seriously. A permanently plumbed natural gas pit removes the tank question entirely, at the cost of a licensed installation and no portability. Wood removes fuel cost entirely, at the cost of smoke, ash, storage and much larger clearance requirements. The tank running out mid-evening is a propane-specific annoyance, and it is worth weighing before you buy rather than in October.
The practical habits
Weigh the tank to know what is left. The tare weight, the empty weight of the cylinder, is stamped on the collar. Put the tank on a bathroom scale, subtract the tare, and what remains is the propane. This is far more reliable than the magnetic strips and the guess-by-lifting method, and it costs nothing.
Keep a spare. Full tanks are cheap insurance against the specific disappointment this page is about.
Close the tank valve when you are finished, not just the pit's control, and do it every time.
Where this article stops
We publish no hours figure, no BTU figure and no cost per evening, because all three depend on your appliance and your fuel price, and a national average would be a fabrication dressed as a fact.
Anything involving the regulator, the hose, the burner assembly or a gas connection is appliance work rather than user maintenance. If the flame is wrong, the fittings are damaged, or you smell gas, that is a gas professional's job.
Frequently asked questions
How many hours does a 20 lb propane tank actually last in a fire pit? There is no universal number, because fire pit BTU ratings differ enormously between products. Divide the total energy in a full tank, about 20 pounds of propane multiplied by propane's published energy content per pound, by your own pit's BTU-per-hour rating from its rating plate or manual. That gives hours at full output, and real use runs below it.
How can I tell how much propane is left in the tank? Weigh it. The tare weight of the empty cylinder is stamped on the collar; put the tank on a bathroom scale and subtract the tare, and what remains is the propane. This is far more reliable than magnetic strips or guessing by lifting.
Why does my propane fire pit weaken in cold weather? Propane has to boil off inside the tank to become gas, and that draws heat from the tank. In cold conditions, especially with a nearly empty tank, the pressure drops and the flame weakens.
Does turning the flame down make the tank last longer? Yes, and it is the single largest variable. Running at half output roughly doubles the hours, and most people turn the flame down after the first ten minutes anyway.
How should the propane tank be stored? Outdoors, upright, in a ventilated place, and never in a basement, a closed garage or indoors, because propane is heavier than air and pools in low spaces. Close the valve at the tank every time you finish, not just the pit's control.
Yard Insight has not run a propane fire pit on its own property and has not measured a burn time, and this article makes no claim otherwise. No hours-per-tank, BTU, or cost figure is stated above, deliberately. The energy content of propane and the tare weight of your cylinder are published figures you can read from your supplier and from the tank collar.
