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How Long Does a Propane Tank Last for a Fire Pit?

A 20 lb tank holds about 430,000 BTU. Divide by your pit's BTU rating and you have the answer — usually four to ten hours. The arithmetic, worked.

By Zakaria 3 min read Save to Pinterest — opens Pinterest in a new tab
A standard 20 lb propane cylinder with its collar handle and service valve, standing on gravel
Photo: Hustvedt, CC BY-SA 3.0, via Wikimedia Commons
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A full 20 lb tank is about 430,000 BTU. Divide by your pit’s BTU-per-hour rating and you have the answer. For most fire pits that lands between four and ten hours at full output — and you will rarely run at full output.

The arithmetic

A 20 lb cylinder is filled to about 4.7 gallons. Propane carries roughly 91,500 BTU per gallon.

4.7 × 91,500 ≈ 430,000 BTU per full tank.

Runtime at full output, 20 lb tank
Pit ratingHours
30,000 BTU/hr~14
40,000 BTU/hr~10.5
50,000 BTU/hr~8.5
60,000 BTU/hr~7
80,000 BTU/hr~5.5
100,000 BTU/hr~4

The rating is on the appliance plate or in the manual. That one number is all you need.

Why real runtime is usually longer

Turning it down is worth more than anything else on this page

Consumption tracks flame height closely, so running at about half output roughly doubles the runtime.

A fire pit is mostly ambience rather than heat output, and most evenings can be spent well below maximum once the pit is warm. That single habit is the difference between a tank lasting two evenings and lasting four.

Checking what is left

  • Warm water down the side. Liquid propane absorbs heat, so the metal is noticeably cooler below the level. Run a hand down and feel for the line
  • Weighing is exact. Every cylinder has its tare weight — the empty weight — stamped on the collar. Current weight minus tare is the propane remaining, in pounds

Tank sizes

Suits
20 lbPortable pits. The usual choice
30–40 lbA pit that lives in one place

Larger tanks run proportionally longer and are heavier to carry and refill, which in practice is the deciding factor rather than runtime.

The cold-weather effect

A cold tank behaves like an empty one

Low temperatures reduce vapour pressure in the cylinder, so less gas is available and the flame runs low — which makes people turn it up and burn through what is left faster.

Do not warm the tank. Start cold evenings with a fuller cylinder instead. If the flame is weak and the tank is not obviously empty, a cold cylinder is one of the usual explanations, alongside a tripped regulator.

Common questions

How long does a 20 lb propane tank last on a fire pit?

Between about four and ten hours on full output, depending entirely on the pit's BTU rating. A standard 20 lb cylinder holds roughly 4.7 gallons of propane, and propane carries about 91,500 BTU per gallon, so a full tank is somewhere near 430,000 BTU. Divide that by the burner rating and you have your runtime: a 50,000 BTU pit gives around eight and a half hours, a 60,000 BTU pit around seven.

How do I work it out for my own fire pit?

Take 430,000 BTU for a full 20 lb tank and divide by the BTU per hour printed on the appliance plate or in the manual. That gives hours at maximum output. Most people do not run a fire pit flat out all evening, so real-world runtime is usually longer than the calculation suggests — often by half again if you turn it down once the pit is warm.

Does turning it down make much difference?

A great deal, because consumption is close to proportional to flame height. Running at roughly half output approximately doubles the runtime. Since a fire pit is mostly about ambience rather than raw heat output, most of an evening can be spent well below maximum, and that is the single biggest lever on how long a tank lasts.

What size tank should I use?

A 20 lb cylinder is the usual choice and suits most portable pits, giving several evenings of typical use. A 30 or 40 lb tank runs proportionally longer and suits a pit that lives in one place. Larger tanks are heavier to move and refill, so the practical question is usually how far you have to carry it rather than how long it lasts.

How can I tell how much propane is left?

Pour warm water down the side of the tank and feel for the cold line — the liquid propane inside absorbs heat, so the metal is noticeably cooler below the level. Weighing is more precise: every cylinder has its empty weight stamped on the collar as the tare weight, so current weight minus tare gives the propane remaining in pounds.

Why does my fire pit seem to use propane faster in winter?

Cold reduces the vapour pressure in the cylinder, so less gas is available and the flame runs lower, which makes people turn it up to compensate. The tank also feels empty sooner than it is. A nearly empty cylinder on a cold night produces a weak flame that mimics a fault, and warming the tank is not safe, so the practical answer is to start cold evenings with a fuller tank.

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