How Long Does a Propane Tank Last on a Fire Pit? Burn-Time Math, Charts & Real-World Answers
If you are wondering how long a propane tank lasts on a fire pit, here is the short answer: a standard 20 lb tank (the kind that fits most patio heaters and gas grills) gives you roughly 7 to 14 hours of burn time. Where you land in that range depends on one number — your burner’s BTU rating — and how high you run the flame on a given night.
This guide gives you two things. First, a quick-answer chart with real runtimes for the most common burner sizes, so you can stop guessing. Second, a simple 4-step method for calculating the exact runtime of your fire pit with your tank, including the adjustments that matter in the real world: flame setting, wind, and cold weather.
The math takes about five minutes and needs no special tools — a bathroom scale helps if you want to check how much fuel is actually in the tank. Let’s get your number.
20 lb Propane Tank: Burn Time by Burner BTU
Find your burner size, read across for your runtime. Assumes a full tank and a full-flame setting.
Based on about 420,000 BTU in a full 20 lb tank (roughly 4.6 gallons × ~91,500 BTU per gallon). Real runtimes vary with flame setting, wind, and temperature.
Safety note before you light up: propane fire pits are outdoor-only appliances. Burning propane in an enclosed space creates a carbon monoxide hazard, so never use one indoors, in a tent, or under a low enclosed roof. Keep the tank upright, outdoors, and ventilated, and keep it away from the fire pit’s heat. If you ever smell gas, turn the valve off, step away, and call your gas supplier or emergency services — do not relight. Also check your local rules: see whether backyard fire pits are legal where you live, and brush up on propane heater safety basics before the season starts.
Calculate Your Exact Runtime in 4 Steps
The chart above covers the common cases. The four steps below give you the precise number for your setup — and once you know the method, you can redo it in your head for any tank or burner.
Read the BTU Rating on Your Fire Pit
Every gas fire pit has a maximum BTU rating printed on a label near the gas inlet, on the underside of the table, or in the owner’s manual. Most residential fire pits fall between 30,000 and 65,000 BTU; large statement burners can reach 100,000 BTU or more. Write the number down — it is the denominator in your runtime math. A bigger number means a taller flame and a shorter tank life.
Weigh Your Tank to Learn How Much Propane Is Inside
A “20 lb” tank holds 20 lb of propane, but the steel tank itself weighs about 17 lb empty. The empty weight (tare weight, stamped “TW” on the tank collar) is your baseline: set the tank on a bathroom scale, subtract the tare weight, and the difference is your fuel. A full 20 lb tank tips the scale at roughly 37–38 lb total. If you have not connected yours yet, see how to hook a propane tank up to a heater for the connection basics.
Divide to Find How Long a Propane Tank Lasts on Your Fire Pit
A full 20 lb tank holds about 420,000 BTU of fuel. Divide that number by your burner’s BTU rating and you get hours of burn time. The formula is the same no matter the tank size — swap in your tank’s BTU content and divide again.
- 420,000 ÷ 30,000 BTU = 14 hours
- 420,000 ÷ 40,000 BTU = 10.5 hours
- 420,000 ÷ 60,000 BTU = 7 hours
Running a smaller 1 lb camping canister instead? It holds roughly 21,500 BTU, so expect about 30–45 minutes on a typical 30,000–40,000 BTU burner — fine for a test, expensive as a habit.
Adjust the Math for Flame Setting, Wind, and Cold
That math assumes a full flame. Turn the control knob down to half and you roughly double your runtime, because the burner is sipping instead of gulping. Wind is the silent tank-killer: gusts blow heat sideways, so you crank the flame higher to feel the same warmth and burn fuel faster. Cold matters too — in freezing weather propane vaporizes more slowly, which can make the flame sag even when fuel remains.
Troubleshooting: When the Tank Runs Out Too Soon
| If This Happens | Try This |
|---|---|
| Tank died way before the math said it would | You may not have started full. Weigh the tank against its tare weight before lighting up — “feels heavy” is not a measurement. Exchange tanks and partially used tanks are the usual culprits. |
| Weak flame even though the tank is full | The regulator’s excess-flow valve may have tripped. Close the tank valve, disconnect the hose for 30 seconds, reconnect, then open the valve slowly. Check the burner ports for spider webs or debris too. |
| Flame shrinks on a cold night with fuel left | Cold slows propane vaporization, so pressure drops. Move the tank out of direct wind (never indoors or into a heated space) and give it time to warm. The fuel is still there — the tank cannot deliver it as fast until it warms up. |
| The built-in gauge says half but the fire dies | Most tank gauges read pressure, not fuel level, and pressure stays misleadingly steady until the end. Trust the scale, not the gauge — weighing against the tare weight is the only honest reading. |
Frequently Asked Questions
Q: Does a lower flame setting really make the tank last longer?
Yes — burn time is nearly proportional to the setting. Half flame for a 40,000 BTU burner behaves like a 20,000 BTU burner, stretching a 20 lb tank toward 20 hours. The table above assumes full blast, which is the worst case.
Q: How can I tell how much propane is left without a scale?
Pour warm (not boiling) water down the side of the tank and feel for the temperature line — the steel feels cool where liquid propane sits and warm above it. It is rough but works in a pinch. For anything precise, weigh the tank.
Q: Is it cheaper to refill or exchange a 20 lb tank?
Refill stations fill the tank to its full capacity, while exchange cages often fill to less — check the net weight printed on the exchange tank’s label. Refilling your own tank at a propane dealer usually gives you more fuel per dollar and keeps a tank you trust.
Q: Can I run my propane fire pit all evening safely?
Yes, as long as it stays outdoors in open air, sits on a non-combustible surface with the clearances in your manual, and is never left unattended. Keep kids and pets at arm’s length from the hot surfaces. Review propane safety basics if this is your first gas appliance.
Q: Do I need a different tank for a fire pit table vs. a freestanding burner?
No — both run on standard 20 lb grill tanks with the same POL/QCC connection. The tank size doesn’t change; only the burner’s BTU rating changes how long a propane tank lasts on a fire pit of either style.
📋 Quick Reference Card
The formula: Tank BTUs ÷ burner BTUs = burn hours
- 20 lb tank ≈ 420,000 BTU of fuel
- 30,000 BTU burner → ~14 hrs
- 40,000 BTU burner → ~10.5 hrs
- 60,000 BTU burner → ~7 hrs
- Full 20 lb tank weighs ~37–38 lb total
Half flame ≈ double the time. Wind and cold shorten it. Weigh the tank — never trust the gauge.
Now you know exactly how long a propane tank lasts on a fire pit — not a guess, but a number you calculated yourself. Grab your burner’s BTU rating, weigh the tank, and run the division before your next gathering so the flame outlasts the conversation.
If you are still weighing gas against wood for your backyard, here’s how to build a classic wood-burning fire pit — the other half of the patio debate.
