Nobody wants the flame to die just as the second round of s’mores comes out. The good news: a standard 20-pound tank runs an average propane fire pit for 3 to 6 hours, and the two things that decide which end of that range you land on are simple, your tank size and your fire pit’s BTU rating. Understand both, and you can plan a tank swap before you ever run dry and stretch every fill further.
TL;DR: A standard 20-lb propane tank lasts 3 to 6 hours on an average fire pit and holds about 4.6 gallons, or roughly 430,000 BTU of energy (U.S. EIA). Burn time rises with a bigger tank and falls with a higher-BTU burner. A 50,000-BTU pit drains a 20-lb tank in about 4 to 7 hours.
A 20-pound propane tank lasts 3 to 6 hours on a typical fire pit, with bigger tanks and lower-BTU burners pushing well past that. The math behind it is steady: one gallon of propane carries 91,452 BTU of energy (U.S. Energy Information Administration), and a filled 20-lb tank holds about 4.6 gallons. That works out to roughly 430,000 BTU per fill, so a 50,000-BTU pit running flat out burns through it in about four to seven hours.
Here is how the common setups shake out:
The pattern is clear: tank size and BTU output do most of the work. How often you run the pit, and how well you maintain it, fill in the rest.
| Tank Size | Fire Pit BTU Rating | Estimated Burn Time |
|---|---|---|
| 20-pound | 20,000 BTU | 8 to 9 hours |
| 20-pound | 50,000 BTU | 3 to 5 hours |
| 30-pound | 50,000 BTU | 5 to 7 hours |
| 40-pound | 60,000 BTU | 6 to 8 hours |
BTU output is the single biggest lever on burn time. BTU stands for British Thermal Unit, the measure of heat your burner throws, and more heat means more propane per hour. A 60,000-BTU model drinks fuel noticeably faster than a 30,000-BTU one, so the flame you choose at purchase shapes every refill that follows.
Four other factors move the needle:
When you estimate your own burn time, pair your tank’s capacity with your fire pit’s BTU rating and then track a few sessions to find your real average. Most pits land within an hour or two of the table above once you know your habits.
Running out mid-evening is avoidable, because every pound of propane you burn equals about 15,000 BTU, so a quick weight check tells you exactly where you stand. Set the tank on a bathroom or kitchen scale, subtract the tare weight stamped near the handle (usually 17 to 18 lbs for a 20-lb cylinder), and what is left is your remaining fuel. Three reliable ways to gauge your level:
Storage matters as much as fuel level. Keep the tank upright and detached from the pit between uses to limit rust, and never store or transport it indoors. Cap the valve to keep out debris, and stash it outdoors in a ventilated spot away from heat and sparks. These habits protect both your runtime and the tank itself.
A portable 20-to-40-lb propane tank lasts 15 to 20 years before metal fatigue becomes a real safety concern, and larger tanks can run safely for 20 to 30 years with care. Inspect portable cylinders at least once a year, and larger tanks over 100 lbs every three to five years. Track the manufacturing date stamped on the collar so you always know the tank’s age.
On each inspection, look for trouble before it finds you. Watch for dents, gouges, bulges, or rust around the valve and seams. For a suspected leak, brush soapy water over the connections and watch for foaming bubbles. And keep an eye on the certification date stamp, since an expired tank cannot be legally refilled until it is requalified.
Pay attention to performance, too. If your runtimes have quietly shortened or you are refilling more often than you used to, a small leak or a failing valve may be the cause. Repeated repairs every couple of years are a signal that replacement is the cheaper, safer call. While you are evaluating the tank, give the pit itself a look. If it is past its prime, our fire pit buyer’s guide walks you through picking the right replacement.
A quality steel or aluminum tank, weighed before each season and inspected yearly, should give you years of clean, smoke-free evenings. Match it to a fire pit sized for your space, and the only thing you will run out of is reasons to go inside.
It depends on the burner’s heat output. A 50,000-BTU pit burns roughly half a gallon of propane per hour, which is why a 20-lb tank lasts about 3 to 6 hours. Lower-BTU models sip far less and stretch much longer on the same tank.
Run the flame lower when you only need ambiance, use a windguard to cut heat loss, and keep the burner clean. Choosing a larger tank or a lower-BTU pit also adds hours. Checking your fuel level before each session prevents the surprise empty that cuts an evening short.
Keep a backup tank on hand so a swap takes two minutes instead of ending the night. Weighing your tank beforehand gives you fair warning, and a spare means you are never choosing between cold and inconvenient.
Andy Wu is the resident backyard products expert and hails from Atlanta, Georgia. His passion for crafting outdoor retreats began in 2003.
As a fellow homeowner, he founded Backyard Oasis to provide top-quality furnishings and equipment, collaborating with leading manufacturers.
His main focus is on sheds and generators!
In his spare time he like to hike the tallest mountains in the world and travel with his family.
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