Propane Tank Runtime Calculator

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Tank:

Custom tank amount:

{{ fillLevelLabel }}:

Exact %

Connected tanks:

tanks

Appliance:

Appliance input:

Runtime is an estimate. Confirm manufacturer data and have a propane professional size the container, regulator, piping, and vapor supply.

BTU/h

Daily use:

The scenario table uses this operating schedule.

Exact h/day

Usable factor:

The default 90% factor is a conservative planning assumption, not an equipment efficiency rating.

Exact %

Reserve fuel:

Reserved fuel is excluded before the usable factor is applied.

Exact %

Lowest tank temperature:

Propane price:

Leave at zero to omit cost context without changing runtime.

$ /gal

Result precision:

Detailed adds one display decimal while leaving canonical values unchanged.

Propane runtime worksheet
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No valid runtime worksheet is available.
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Propane use scenarios
Planning horizon	Burn time	Fuel needed	Tank sets	Copy
No valid use scenarios are available.
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A propane container can hold enough fuel for many hours and still fail to supply a high-demand appliance in cold weather. Stored energy and vapor-delivery capacity are separate questions. Runtime asks how long the fuel can last; vaporization asks whether liquid propane can turn into vapor fast enough for the regulator and burner at the current temperature.

Container labels also use different kinds of capacity. Portable cylinders are commonly named by the propane weight they can hold, such as a 20 lb grill cylinder. Larger tanks are often described by water capacity or nominal tank gallons, with liquid propane limited to a fraction of that volume to leave expansion space. A gauge percentage on a stationary tank is not the same thing as pounds on a cylinder.

Fuel amount sets the gross energy available.
Appliance input in BTU/h sets the rate at which fuel energy is consumed.
Reserve deliberately keeps part of the fuel outside the runtime plan.
Usable factor reduces the remaining energy for field uncertainty, cycling, or incomplete use.
Daily use turns continuous burn hours into calendar days without changing total burn time.

British thermal units per hour (BTU/h) must come from the appliance fuel-input rating, not its useful heat output, room size, electrical rating, or advertised coverage. If several burners or appliances run from the same supply, use their simultaneous input when the goal is to size the fuel demand.

A reserve protects the plan from running right to empty, but it does not improve vapor flow. Temperature, tank surface area, liquid level, and connected-container arrangement affect vaporization. Small cylinders and custom tank sizes need manufacturer or supplier data because a general energy calculation cannot confirm regulator capacity or cold-weather delivery.

Runtime is never a safety approval. Propane appliances require correct location, ventilation, combustion air, regulators, hoses, leak checks, clearances, and carbon-monoxide precautions. Follow the appliance and container instructions and use a qualified propane professional for permanent, indoor, RV, generator, manifold, or high-load installations.

How to Use This Tool:

Match the tank basis and appliance input first; reserve, daily use, temperature, and price refine different parts of the result.

Choose the closest Tank preset, then enter current fill and the number of tanks feeding the same load. For a custom amount, distinguish rated propane pounds, actual propane gallons, and water-capacity gallons.
Select an appliance, then replace Appliance input with its nameplate BTU/h value. Add simultaneous appliance inputs before entering a shared load.
Set Daily use, Usable factor, and Reserve fuel. Enter the lowest expected tank temperature when the limited vapor-flow reference applies.
Read continuous runtime and calendar days separately. If the vapor result is below the reference or unavailable, check supplier sizing data instead of treating fuel quantity as proof that the appliance can run.

Interpreting Results:

Runtime hours is continuous burn time after reserve and usable factor. Thermostat cycling or partial burner use can stretch calendar time, but only if the average fuel input is lower than the entered load.
Calendar days equals runtime hours divided by daily use. It is a schedule estimate, not a guaranteed refill date.
Reserve hours reports the theoretical burn time represented by the reserved share of gross energy. That reserve is excluded from planned runtime.
Meets reference means the limited continuous vapor-capacity reference is at least equal to the entered load. Below reference needs supplier or installer review.
Not available does not mean safe or unsafe. It means the current tank, fill, or temperature falls outside the available 250/500-gallon reference lookup.

Technical Details:

The energy path depends on how tank capacity is expressed. Pound-capacity cylinders use 21,548 BTU per pound for gross energy and 4.2 lb per gallon for the displayed fuel conversion. Gallon and water-capacity entries use 91,502 BTU per gallon. These constants are applied as separate source values rather than forcing one to be derived from another.

Formula Core:

Let W be propane pounds, G propane gallons, n connected tanks, r reserve rate, u usable factor, L appliance input in BTU/h, and d daily use in hours.

\begin{array}{ll} E_{lb} & = W \times 21548 \times n \\ E_{gal} & = G \times 91502 \times n \\ E_{usable} & = E_{gross} \times (1 - r) \times u \\ T & = \frac{E_{usable}}{L} \\ Calendar days & = \frac{T}{d} \end{array}

For a pound-capacity cylinder, propane pounds equal rated pounds × fill percentage. Displayed gallons equal pounds ÷ 4.2. For actual propane gallons, the entered amount is multiplied by fill percentage. For water-capacity gallons, nominal gallons are likewise multiplied by fill percentage, which is limited to 80%.

Burn rate in gallons per hour is appliance BTU/h ÷ 91,502. Burn rate in pounds per hour is appliance BTU/h ÷ 21,548. Fuel cost per hour uses the gallons-per-hour rate and the entered price. Price changes cost results only; it does not change runtime.

Lookup Core:

The vapor screen uses continuous capacity equal to 25% of the referenced intermittent capacity, multiplied by connected tank count. Temperature is converted to Fahrenheit, rounded down to the next 10°F band from −30°F through 40°F, and capped at 40°F.

Continuous propane vapor-capacity reference used by the calculator
Temperature band	250 gal tank	500 gal tank
−30°F	35,875 BTU/h	59,650 BTU/h
−20°F	36,450 BTU/h	60,575 BTU/h
−10°F	44,350 BTU/h	73,700 BTU/h
0°F	45,150 BTU/h	75,025 BTU/h
10°F	49,600 BTU/h	82,425 BTU/h
20°F	54,200 BTU/h	90,100 BTU/h
30°F	62,950 BTU/h	104,650 BTU/h
40°F or warmer	72,025 BTU/h	119,700 BTU/h

Rule Core:

The vapor lookup is available only for the 250- or 500-gallon water-capacity presets, at a fill of at least 50%, and at −30°F or warmer. It does not interpolate for custom tanks or other sizes. Capacity divided by appliance input gives the reference ratio; a ratio of at least 1 is Meets reference, while a ratio below 1 is Below reference.

Load-curve runtime is calculated at 50%, 75%, 100%, 125%, 150%, and 200% of the entered appliance input. Scenario fuel needs use the daily schedule and usable factor but do not subtract the reserve again. Results retain full calculation precision and are formatted to the selected display precision.

Safety and Accuracy Notes:

Use this estimate for refill and fuel planning only. Do not use it to approve an installation or override appliance, cylinder, regulator, or local-code requirements.

Exchange cylinders and partly filled tanks may contain less propane than the rated capacity or gauge suggests.
Real use changes with burner settings, thermostat cycling, generator load, ambient conditions, regulator performance, and gauge accuracy.
A tank can contain liquid propane but fail to vaporize it fast enough in cold weather.
Never bring outdoor propane appliances indoors. Follow carbon-monoxide, ventilation, leak-testing, storage, and clearance instructions.
Ask a propane supplier or qualified installer to size high-load, permanent, manifolded, RV, or cold-weather systems.

Worked Examples:

20 lb grill cylinder

A full 20 lb cylinder contains 430,960 BTU by the pound-based constant. Holding 10% in reserve and applying a 90% usable factor leaves 349,077.6 BTU for planning. At 35,000 BTU/h, runtime is about 9.97 burn hours, or just under five days at two hours per day. No vapor reference is available for this cylinder size.

250 gallon tank at 0°F

A 250-gallon water-capacity tank at 60% contains 150 gallons of propane. With no reserve and a 100% usable factor, a 35,000 BTU/h load has about 392.15 hours of modeled energy runtime. The continuous reference at 0°F is 45,150 BTU/h, giving a ratio of 1.29 and a Meets reference result for that limited check.

References:

Technical Pocket Guide, Propane Education & Research Council.
CPSC helps make grills safer, U.S. Consumer Product Safety Commission.