Estimated runtime--
Propane Tank Runtime Calculator
Estimate how long a propane tank will run a heater, grill, stove, or generator from tank size and BTU load.
How to use this calculator
Enter the measurements or usage numbers you know, then use the result as a planning estimate. The defaults are realistic starting points, but the best result comes from replacing them with your actual product, property, trip, or equipment numbers.
Practical planning tips
- Add a reserve for waste, weather, terrain, load, or product variation.
- Check labels, local codes, manufacturer charts, and safety requirements before buying materials or operating equipment.
- Round up when a shortage would stop the job, trip, or chore.
FAQ
Propane Tank Runtime Calculator questions
Can I use this result for buying materials?
Use it as a planning estimate, then verify against product coverage, local requirements, and the conditions on your property or trip.
Why should I add a reserve?
Real projects and outdoor conditions rarely match the perfect math. A small reserve helps cover waste, uneven ground, spills, weather, and user input error.
Propane runtime planning overview
This propane tank runtime calculator estimates how long a propane tank may run a heater, grill, generator, RV appliance, shop heater, or other BTU-rated load. It helps compare tank sizes and understand why cold weather or high demand can shorten useful runtime.
The result supports fuel planning, refill timing, tank comparison, appliance scheduling, and emergency preparation. A propane estimate is only useful when the tank amount, appliance BTU rating, regulator capacity, and conditions are realistic.
Inputs explained
Tank size describes the fuel supply. BTU load describes how quickly the appliance consumes energy. Reserve protects against empty-tank planning and measurement error. If an appliance cycles on and off, average load is more useful than maximum burner rating.
Formula or method
Propane energy = usable gallons x about 91,500 BTU per gallon.
Runtime hours = usable BTU divided by appliance BTU per hour.
Usable fuel = tank amount x (1 - reserve percent).
One gallon of propane weighs about 4.24 lb.
Some tanks are labeled in pounds and others in gallons. A standard 20 lb cylinder holds about 4.7 gallons when filled correctly, but exchange cylinders may contain less depending on the supplier.
Worked example
A 20 lb cylinder with about 4.7 gallons contains roughly 430,000 BTU before reserve. With a 10 percent reserve, usable energy is about 387,000 BTU. A 30,000 BTU per hour heater running continuously would last about 12.9 hours under those assumptions.
How to interpret the result
Round down for runtime when heat, refrigeration, or power matters. Round up for fuel planning only when storage rules, ventilation, and tank handling are safe. Cold cylinders may vaporize propane too slowly for high-demand appliances.
Common mistakes
- Assuming an exchange cylinder always contains the same propane as a fully filled cylinder.
- Using maximum BTU input when average cycling load would be more realistic.
- Ignoring cold-weather vaporization limits.
- Running outdoor-rated propane appliances inside enclosed areas.
- Planning no reserve when weather, refills, or access may change.
Trust and disclaimer note
Propane appliances can create fire, explosion, oxygen depletion, and carbon monoxide hazards. Follow the appliance manual, tank label, regulator requirements, ventilation instructions, manufacturer specs, and local rules. Do not use outdoor-only propane appliances indoors.
FAQ
Propane tank runtime questions
How many BTU are in a gallon of propane?
A common planning value is about 91,500 BTU per gallon.
Why does cold weather reduce performance?
Cold tanks vaporize propane more slowly, so high-demand appliances may starve for fuel.
Can I use this for indoor heaters?
Only use appliances in the way the manufacturer allows. Outdoor-only propane appliances should not be used indoors.
Should I include a reserve?
Yes. Reserve helps cover gauge error, exchange fill differences, cold weather, and refill delays.
Does this replace manufacturer specs?
No. Verify with the appliance manual, regulator rating, tank label, and local requirements.
Realistic propane runtime examples
Patio heater on a 20 lb cylinder
A patio heater rated at 40,000 BTU per hour is connected to a 20 lb cylinder. A full 20 lb cylinder is roughly 4.7 gallons, or about 430,000 BTU before reserve. At 90 percent usable fuel, the practical energy is about 387,000 BTU, which gives roughly 9.7 hours if the heater runs continuously on high.
RV furnace cycling overnight
An RV furnace rated at 30,000 BTU per hour does not usually run every minute. If cold weather makes it run about half the time, the average load is closer to 15,000 BTU per hour. A 30 lb cylinder with about 7 gallons can provide about 576,000 usable BTU at 90 percent, or about 38 hours at that average load.
Practical propane runtime tips
- Use average BTU load for appliances that cycle instead of assuming the burner runs nonstop.
- Expect shorter useful runtime in very cold weather because cylinders vaporize propane more slowly.
- Check whether an exchange cylinder contains less propane than a fully refilled cylinder.
- Keep tanks upright, protected from heat, and used only with the correct regulator and hose.
- Round runtime down when propane is needed for heat, cooking, refrigeration, or emergency power.
What number should I use?
Use measured inputs first
Start with the actual number from your project, device, network, trip, or equipment label instead of a best guess.
Round in the safer direction
Round up for materials, food, water, storage, and capacity. Round down for runtime when running short would cause trouble.
Check related tools
Use the related calculators on this page to plan the next part of the job instead of treating one result as the whole answer.