Propane Tank Duration Calculator
Find out how long your propane will last. Pick the tank size and how full it is, add the appliance's BTU rating and how many hours a day you use it, and see the burn time, the days until empty and what a refill costs.
Last updated:
Cylinders: % of a full tank. Large tanks: the gauge reading (a full tank reads about 80%).
Edit to your local price. Cylinder exchanges cost more per gallon than refills.
From the rating plate or manual.
100% = all burners on high. Medium heat or a cycling thermostat is often 40-70%.
How to use the Propane Tank Duration Calculator
- Choose the tank and enter how full it is (cylinder % or the large-tank gauge reading).
- Enter your propane price per gallon (optional, for cost results).
- Pick the appliance or enter its BTU/hr rating from the data plate.
- Enter hours per day and the average setting, then add a second appliance if needed.
- Read how long the propane lasts, the burn time and the refill cost, and compare tank sizes in the table.
Propane duration formula
Hours of burn time = propane in the tank (BTU) ÷ appliance use (BTU per hour)
- 1 gallon of propane ≈ 91,452 BTU and weighs about 4.24 lb
- 1 lb of propane ≈ 21,548 BTU
- Appliance use = rated BTU/hr × average setting (for example 75% for medium-high)
- Days = BTU in the tank ÷ (BTU/hr × hours used per day)
Example: a full 20 lb tank holds 20 × 21,548 = 430,960 BTU. A 36,000 BTU/hr grill at 75% uses 27,000 BTU/hr, so the tank gives 430,960 ÷ 27,000 = 16 hours of grilling, or about 16 days at one hour a day.
Propane tank sizes
| Tank | Propane when full | Energy | Hours at 10,000 BTU/hr | Typical use |
|---|---|---|---|---|
| 20 lb cylinder | 4.7 gal (20 lb) | 431,000 BTU | 43 | Grills, patio heaters, fire pits |
| 30 lb cylinder | 7.1 gal (30 lb) | 646,000 BTU | 65 | RVs, campers |
| 40 lb cylinder | 9.4 gal (40 lb) | 862,000 BTU | 86 | RVs, construction heaters |
| 100 lb cylinder | 23.6 gal (100 lb) | 2.15 million BTU | 215 | Small homes, cabins, generators |
| 120 gal tank | 96 gal (at 80%) | 8.8 million BTU | 878 | Water heater, range, dryer |
| 250 gal tank | 200 gal | 18.3 million BTU | 1,829 | Small home heating |
| 500 gal tank | 400 gal | 36.6 million BTU | 3,658 | Whole-home heating |
| 1,000 gal tank | 800 gal | 73.2 million BTU | 7,316 | Large homes, farms, businesses |
Tips to make propane last longer
- Weigh cylinders to know the real level: subtract the tare weight (TW) stamped on the collar from the total weight to get the pounds of propane left.
- Use lower settings. Grilling with the lid closed and only the burners you need cuts gas use noticeably.
- Shelter patio heaters and fire pits from wind, which carries heat away and tempts you to turn them up.
- Service furnaces and water heaters and lower the thermostat a few degrees at night or when away.
- Refill rather than exchange when you can: exchange cylinders are often not completely full, so the price per gallon is higher.
- Use propane appliances safely: never run grills, patio heaters or outdoor heaters indoors or in a closed garage, and keep a carbon monoxide alarm near any indoor gas appliance.
Frequently asked questions
How long does a 20 lb propane tank last?
A full 20 lb tank holds about 4.7 gallons, or roughly 430,000 BTU. On a 36,000 BTU/hr grill running at full power that is about 12 hours; at a medium setting it is closer to 16-20 hours. A 40,000 BTU patio heater on high uses a 20 lb tank in about 10-11 hours.
How do I calculate propane burn time?
Burn time in hours = BTU in the tank ÷ the appliance's BTU per hour. One gallon of propane contains about 91,452 BTU and one pound about 21,548 BTU. Multiply the gallons in the tank by 91,452 and divide by the appliance rating multiplied by its average setting.
Why is a 500 gallon propane tank only filled to 400 gallons?
Large propane tanks are filled to about 80% of their water capacity, leaving space for the liquid to expand as it warms. The gauge on a large tank reads percent of the total capacity, so 80% means full and 40% on a 500 gallon tank means about 200 gallons.
How much propane does a furnace use?
A furnace uses its BTU rating divided by 91,452 gallons per hour while the burner is on. An 80,000 BTU/hr furnace burns about 0.87 gallons per hour of run time. How many hours it runs depends on the weather, the home's insulation and the thermostat setting.
How many gallons are in a 20 lb propane tank?
About 4.7 gallons. Propane weighs about 4.24 lb per gallon, so 20 ÷ 4.24 = 4.7. A 30 lb cylinder holds about 7.1 gallons, a 40 lb about 9.4 gallons and a 100 lb about 23.6 gallons.
Is the result exact?
No, it is an estimate. Appliances rarely run at full rating all the time, gauges are approximate, and very cold weather reduces how fast a small tank can supply gas. Use the result to plan refills and keep a spare cylinder for cooking or heating you depend on.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.