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A 1 lb propane cylinder holds a fixed amount of fuel. How long it lasts depends entirely on your heater’s BTU output. Here is the formula, and a table across the BTU ratings most portable heaters actually use.
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The Formula
One pound of propane holds roughly 21,600 BTU of usable energy. This is a standard, widely published conversion, not specific to any single brand. To find run time in hours, divide 21,600 by your heater’s BTU rating. A 3,800 BTU heater works out to roughly 5.7 hours. A 9,000 BTU heater works out to roughly 2.4 hours. Higher output burns through the same amount of fuel faster, every time.
Run Time by BTU Rating
- 3,800 BTU: roughly 5.7 hours
- 9,000 BTU: roughly 2.4 hours
- 11,000 BTU: roughly 2 hours
- 12,000 BTU: roughly 1.8 hours
- 18,000 BTU: roughly 1.2 hours
These are full-burn estimates at maximum output. Real-world run time is often a bit longer, since most heaters cycle rather than running flat-out the entire time. For the Mr. Heater Buddy lineup specifically, our Buddy-specific run time table covers every model and setting in one place.
Why This Table Works for Any Brand
The 21,600 BTU-per-pound figure is a property of propane itself, not a brand-specific spec. Any heater that runs on a 1 lb cylinder, regardless of manufacturer, follows the same math. If your heater’s BTU rating is not on the list above, take the 21,600 figure and divide it by your heater’s specific output to get your own number.
Does Cold Weather Change the Math?
Slightly, in genuinely cold conditions. Propane vaporizes a little less readily as temperature drops, which can shave a small amount off real-world run time compared to the flat calculation. This effect is minor under normal winter conditions and becomes more noticeable only in extreme cold. Packing one extra cylinder beyond your calculated need is a simple way to build in a margin.
How to Tell How Much Fuel Is Left
Disposable 1 lb cylinders have no built-in gauge, which makes judging remaining fuel hard mid-use. Some people partially submerge a cylinder in water. The fuel level sits at a different temperature than the empty space above it, which is sometimes detectable by touch. This is only a rough approximation. Packing a spare cylinder is more reliable than trying to estimate exactly how much is left.
Why Manufacturer Numbers Sometimes Differ Slightly
Some manufacturer literature quotes a slightly different run-time figure than the plain math above. This usually happens because a published number reflects an average across a full burn cycle, rather than a peak instantaneous rate, or because it was tested at a specific ambient temperature. Altitude, temperature and even how full a cylinder was at the start of a burn can shift real-world numbers by a small margin either way. Treat any run-time figure, including the ones on this page, as a solid planning estimate rather than a lab-precise promise.
Packing Enough Cylinders for a Trip
Work backward from your expected hours of use per day, using the table above for your heater’s BTU rating. A heater run for four hours a night on a 9,000 BTU setting burns through close to two 1 lb cylinders per night. Multiply that by the number of nights on your trip, then add at least one spare cylinder beyond the calculated total. A cold snap, an extra night, or running slightly hotter than planned can all eat into your margin faster than expected, and the cost of one spare cylinder is small next to running out of heat.
When 1 lb Cylinders Stop Making Sense
For a single evening’s use, 1 lb cylinders are simple and portable. For a heater run for hours at a time, regularly, the math shifts. A 20 lb tank holds roughly 20 times the fuel of a single 1 lb cylinder, at a lower cost per hour of use. Our 20 lb tank run-time guide covers that comparison, and our tanks and accessories guide covers the hose-and-adapter kits that make the switch possible.
Refillable vs. Disposable 1 lb Cylinders
Standard 1 lb cylinders are single-use and get discarded once empty, but refillable versions exist and can be topped off from a larger 20 lb tank using an adapter. A refillable cylinder costs more upfront than a disposable one, but it pays for itself over repeated use, since refilling from a 20 lb tank costs a fraction of buying disposable cylinders one at a time. This is a popular upgrade for hunters, campers, and anyone using a small radiant heater often rather than occasionally, since the same 1 lb cylinder gets reused dozens of times instead of thrown away after a single trip.
Storing Partly Used Cylinders Between Trips
A 1 lb cylinder that isn’t fully empty can be stored and used again on a future trip, as long as it’s kept upright in a cool, dry, well-ventilated spot away from direct heat sources. There’s no real shelf life concern with the propane itself sitting in a sealed cylinder, but the cylinder’s own condition matters — check for dents, rust or valve damage before reusing one that’s been sitting for a season or more. Marking a partly used cylinder somehow, even just setting it apart from full ones, avoids the common mistake of grabbing what you think is a full cylinder only to find it runs out halfway through a trip.
Disposing of an Empty Cylinder Safely
An empty disposable 1 lb cylinder should never go in regular household trash or recycling, even once it feels completely spent, since a small amount of residual propane can remain inside. Many hardware stores, propane retailers and household hazardous waste facilities accept empty cylinders for proper disposal or recycling. Some retailers also offer a cylinder exchange or refill program that takes an old one off your hands as part of the transaction. Check your local municipality’s hazardous waste guidance if you’re unsure, rather than assuming an empty cylinder is safe for curbside pickup.
Propane Run-Time Calculator
Estimate how long a tank will last. Real-world run time varies with weather, altitude and burner setting.