Propane Tank Runtime Calculator

Tank preset:

Use the common size closest to your tank, or choose custom to enter propane pounds or gallons.

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Connected tanks:

Multiple connected tanks multiply stored fuel and raise the rough vaporization screen.

tanks

Appliance preset:

Presets are starting points only. The BTU per hour input below is the value used in the runtime math.

Appliance input:

Runtime equals usable propane BTU divided by this BTU per hour load.

BTU/h

Use per day:

Use pattern for days-to-empty and tank-count planning.

h/day

Usable factor:

A 90% factor is a conservative field estimate for many portable setups.

Reserve fuel:

Runtime is calculated after this reserve is subtracted from current propane on hand.

Check the propane runtime inputs

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Custom tank amount:

For nominal bulk gallons, the fill slider uses the tank gauge percent.

Tank temperature:

Cold tanks may not vaporize propane fast enough for high BTU loads even when fuel remains.

Propane price:

Cost fields do not change runtime; they estimate fuel value and cost per burn hour.

$ /gal

Display precision:

Use more decimals for small cylinders or short test burns.

Runtime ledger
Metric	Value	Planning note	Copy
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Propane use plan
Scenario	Burn hours	Tank sets	Fuel needed	Copy
{{ row.scenario }}	{{ row.burnHours }}	{{ row.tankSets }}	{{ row.fuelNeeded }}

Vaporization screen
Check	Signal	Action	Copy
{{ row.check }}	{{ row.signal }}	{{ row.action }}

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Propane runtime is an energy balance: the fuel on hand supplies a fixed number of BTUs, and the appliance consumes those BTUs at a rated input per hour. A small cylinder can run a grill for an evening, while the same cylinder may not support a large heater or generator for very long. Runtime changes quickly when fill level, connected tanks, reserve fuel, appliance load, and daily use pattern change.

Planning is also more practical than a simple tank-size division. A reserve may be needed for pressure margin or a scheduled refill, real equipment may not operate at ideal efficiency, and cold cylinders can have vaporization limits even when liquid propane remains. For portable cylinders, capacity is commonly expressed in pounds of propane. For bulk tanks, the gauge reading is usually a percent of nominal water capacity, with normal fills below the full shell volume.

A good runtime estimate keeps those assumptions visible. It converts tank capacity and fill into gallons and pounds, applies reserve and usable-factor derates, divides by the appliance input rating, and then checks whether the connected tank setup is likely to provide enough vapor flow for the load.

Stored propane energy is divided by appliance BTU per hour, with reserve and vapor flow checks. — The runtime chain starts with usable propane energy, then applies appliance load, daily use, reserve, and vapor-flow assumptions.

How to Use:

Select the closest tank preset, or use a custom tank amount when you know the propane capacity in pounds or gallons.
Enter the fill level. For portable cylinders, 100% means the rated propane weight. For bulk tanks, use the gauge reading.
Set the number of connected tanks when several cylinders or bulk tanks feed the same appliance or manifold.
Choose an appliance preset, then override the BTU/h field with the nameplate input rating when you know the actual load.
Enter hours of use per day to convert total burn hours into calendar days.
Adjust usable factor, reserve fuel, tank temperature, propane price, and display precision for field planning, cost estimates, and the vaporization screen.

Interpreting Results:

Runtime Ledger shows propane gallons, pounds, gross BTUs, reserve, usable BTUs, burn hours, daily runtime, fuel cost, and cost per hour.
Use Plan translates the result into practical refill timing and tank-count planning.
Vapor Check compares the appliance load with a rough tank vaporization capacity estimate for the selected tank setup and temperature.
Runtime Load Chart shows how runtime changes as appliance input increases or decreases around the current load.
JSON records the normalized tank, appliance, reserve, cost, and runtime fields for service notes or trip planning.

Technical Details:

The runtime calculation converts all tank presets to propane gallons and pounds. It uses 91,452 BTU per gallon of propane and 4.24 pounds per gallon. Reserve fuel is subtracted before the usable-factor derate, so the result reflects a planned buffer rather than running the tank to empty. Bulk tank presets use the tank gauge percentage against nominal gallons, while portable cylinder presets use the cylinder's rated propane weight.

Formula Core:

gross_BTU = propane_gallons \times 91452

usable_BTU = gross_BTU \times (1 - reserve_fraction) \times usable_factor

runtime_hours = \frac{usable_BTU}{appliance_BTU_per_hour}

calendar_days = \frac{runtime_hours}{hours_per_day}

Fuel cost is calculated from gallons consumed per hour and the entered propane price. The vapor screen multiplies the selected tank's base vapor capacity by tank count and derates it for fill and temperature conditions.

Safety And Accuracy Notes:

Use the appliance input rating in BTU/h, not heated space, burner diameter, or output temperature.
Runtime estimates do not confirm regulator sizing, hose sizing, ventilation, combustion safety, carbon-monoxide safety, or code compliance.
Cold weather can reduce vaporization capacity. A tank may contain fuel but still fail to sustain a high-BTU appliance.
Exchange cylinders, refilled cylinders, and bulk tanks may not contain exactly the nominal amount assumed by the preset.
For indoor, RV, generator, heater, or commercial use, follow the appliance manual and local fuel-gas requirements.

Worked Examples:

Scenario	Input Focus	Planning Readout
20 lb grill cylinder	100% fill, 35,000 BTU/h grill, 2 hours per day, 10% reserve, 90% usable factor.	Shows whether one cylinder is enough for several cooking sessions before a refill or spare cylinder is needed.
Patio heater evening	48,000 BTU/h load and a higher daily use window.	Highlights that a high-output heater can consume a common portable cylinder much faster than a grill.
Bulk tank appliance	Gauge percent, nominal tank gallons, continuous daily use, and tank temperature.	Estimates days to refill threshold and checks whether vapor flow is likely to be a constraint.

FAQ:

Why does a 20 lb cylinder show less than 5 gallons?

Propane weighs about 4.24 lb per gallon, so 20 lb of propane is roughly 4.7 gallons. The cylinder shell itself weighs more and is not part of the fuel amount.

What does usable factor represent?

It is a practical derate for cycling, cold weather, appliance variation, pressure losses, and field uncertainty. Set it to 100% only for ideal steady-state math.

Can this confirm that a propane setup is safe?

No. It estimates fuel runtime and flags rough vapor-flow risk. It does not inspect regulators, hoses, ventilation, appliance certification, or installation requirements.

Glossary:

BTU: British thermal unit, a unit of heat energy used for fuel content and appliance input ratings.
BTU/h: The rate at which an appliance consumes fuel energy per hour.
Reserve fuel: Fuel intentionally held back for pressure margin, refill planning, or tank changeover.
Usable factor: A derate applied after reserve to account for field conditions and uncertainty.
Vaporization capacity: The tank's rough ability to turn liquid propane into vapor quickly enough for the appliance load.