How Long Does a Propane Tank Last on a Grill?

The calculation, and the two numbers in it

Propane is sold by weight and burners are rated in BTU per hour, so the conversion between them is the whole problem. Two figures solve it.

The first is how much energy is in the tank. The standard cylinder everybody calls a “20 lb tank” is named for the weight of propane it holds when properly filled: 20 pounds. Propane’s energy content is about 21,500 BTU per pound— a published physical property of the fuel, not an estimate of ours, and you can check it against any propane supplier’s data sheet. Twenty pounds at 21,500 gives roughly 430,000 BTU in a full tank.

The second is how fast your grill burns it, which is the BTU figure printed on the listing. That number is a rate: BTU per hour at full output. So:

430,000 ÷ main burner BTU = hours at full blast

That is the floor, and it is useful precisely because it is the worst case. If your grill will run for nine hours with every burner wide open, it will never run out in the middle of a steak.

The arithmetic on every gas cooker we track

Each row uses the manufacturer’s own published burner rating, the same figure quoted in that product’s card on this site. Where a maker publishes a total rather than a main-burner output, the row says so — and where a maker publishes nothing usable, the row is blank rather than guessed at.

The last two rows are the interesting ones. Char-Broil publishes a side-burner rating and a total cooking area but not a main burner output, so there is no honest way to calculate its tank life — the same gap that makes it impossible to compute its BTU per square inch in our BTU guide. And the Genesis S-435 in our registry is the natural gas version: plumbed to the house line, it never uses a tank at all, which is the one configuration that makes this entire page irrelevant.

Why “typical” is roughly double

The full-output column assumes every burner on maximum for the entire time, and nobody cooks that way. A realistic cookout looks like ten to fifteen minutes of preheating with everything on high, then one or two burners on medium while food cooks, often with a burner off entirely to create an indirect zone. Averaged across a session, most grills draw somewhere around half their rated output.

That is where the familiar “a tank lasts about 18 to 20 hours” figure comes from, and why the common rule of thumb — roughly 20 cookouts per tank— holds up for a typical three-burner used for about an hour at a time. Scale it to your own grill using the table: a Napoleon Prestige 500 is meaningfully thirstier than a Weber Spirit, and a 60,000 BTU griddle is thirstier still.

Three things push you back toward the worst-case column. Cold weatheris the big one: propane’s vapour pressure falls as temperature drops, so a tank in freezing conditions delivers gas more slowly and the grill works harder and longer to reach temperature. Wind strips heat off the firebox continuously. And searing or griddling at full output, as opposed to grilling at medium, is exactly the scenario the first column describes.

How to tell how much is left

A propane tank has no fuel gauge because the propane inside is a liquid under its own pressure, and pressure stays almost constant until the liquid is gone. A pressure gauge therefore reads “full” right up until it reads “empty,” which is why the inexpensive screw-on dial gauges are so unsatisfying. Three methods actually work.

1. Weigh it. This is the only precise method and it needs no equipment beyond bathroom scales. Stamped on the collar of every cylinder is a tare weight — usually marked TW— which is the weight of the empty tank. Weigh the tank, subtract the tare weight, and the remainder is pounds of propane left. Multiply by 21,500 for the BTU remaining, or just compare it to 20: half the number means half a tank.

2. The hot water trick. Pour a jug of warm water down one side of the tank, then run your hand down the same side. The liquid propane absorbs heat from the water, so the metal feels cool where there is still liquid behind it and warm where there is only vapour. The boundary you can feel is the fuel level. It takes thirty seconds and gets you within an inch or two.

3. Own a second tank. This is the real answer and the one everyone arrives at eventually. A spare tank costs far less than ruining a dinner, removes the problem entirely, and means you only ever refill at your convenience. If you own a grill and do not own a spare cylinder, that is the single highest-value purchase in this whole category.

Refill or exchange?

Both work and they are not equivalent. Refilling at a propane dealer charges you by the gallon and fills your cylinder properly, so you get a genuinely full tank and you keep your own cylinder. Exchange cagesat hardware stores and gas stations swap your cylinder for a pre-filled one in about ninety seconds, which is far more convenient — but exchange tanks are commonly filled to less than the cylinder’s nominal capacity, so you may be paying a comparable price for noticeably less gas. Check the stated fill weight on the exchange cage.

One thing exchange does handle for you: cylinder age. Every US propane cylinder carries a manufacture date stamped on the collar and has a limited service life before it must be requalified, after which refill stations will refuse it. An exchange program takes the old cylinder off your hands and gives you a current one, which is a real and underrated advantage if yours has been in the garage for a decade. If you refill, check the stamp.

Running a grill from a small camping bottle

Portables and tabletop griddles are often designed around the 1 lb camping cylinder, and the arithmetic there is brutal: one pound of propane is about 21,500 BTU, so a 12,500 BTU tabletop griddle gets roughly an hour and three quarters out of a bottle at full output, and a 24,000 BTU one gets under an hour. That is fine for a campsite breakfast and expensive and inconvenient as a routine.

An adapter hose that connects a portable to a standard 20 lb tank is therefore one of the better accessory purchases for anyone using a tabletop cooker at home — twenty times the fuel at a fraction of the cost per pound. The catch is storage, and if you are cooking on a balcony it may be the binding constraint; we cover that trade in best grills for small patios and balconies.

Safety points that are actually worth the words

• Store tanks outdoors and upright, never indoors or in a basement. Propane is heavier than air, so a leak in an enclosed space pools at floor level rather than dispersing. A garage is a poor second choice; outside and shaded is right.
• Check the connection with soapy water, not a flame. Brush soapy water on the hose and regulator connection with the valve open; growing bubbles mean a leak. Tighten, or replace the hose.
• Open the tank valve slowly.Modern cylinders have an overfill protection device that can trip on a fast surge of flow and restrict gas to a trickle — which presents exactly as “my grill will not get hot any more.” If that happens, turn everything off, close the tank, wait a minute and reopen the valve slowly before relighting.
• Turn the tank off, not just the burners. Close the cylinder valve at the end of every cook. It costs nothing and it is the one habit that makes a hose failure a non-event.

Where to go next

If the BTU figure on your grill’s listing is the number you are trying to make sense of, how many BTUs a gas grill needsis the companion to this page — it divides the same rating by cooking area instead of into tank capacity, and explains why a bigger number is often a worse grill. For what actually matters when buying, the gas grill buying guide covers grates, build and warranty, and how to use a gas grill sets up the two-zone method that is also, incidentally, the cheapest way to run one.