Track greenhouse, patio, and standby propane consumption easily. Adjust duty cycle, reserve, and equipment loads. Keep garden projects running longer without waste or surprises.
These sample values assume 80% fill, 10% reserve, 100% duty cycle, 100% delivery efficiency, and one 35,000 BTU/hour appliance.
| Tank | Approx Gallons | Load BTU/hour | Runtime Hours |
|---|---|---|---|
| 20 lb cylinder | 4.72 | 35,000 | 8.89 |
| 30 lb cylinder | 7.08 | 35,000 | 13.33 |
| 40 lb cylinder | 9.44 | 35,000 | 17.78 |
| 100 lb cylinder | 23.60 | 35,000 | 44.45 |
| 120 gallon tank | 120.00 | 35,000 | 225.98 |
| 250 gallon tank | 250.00 | 35,000 | 470.79 |
1. Equivalent tank gallons = tank pounds ÷ propane density
2. Filled gallons = equivalent gallons × fill level
3. Reserve gallons = filled gallons × reserve percentage
4. Usable gallons = filled gallons − reserve gallons
5. Available BTUs = usable gallons × 91,500 × delivery efficiency
6. Effective load = appliance load × appliance count × duty cycle × seasonal demand factor
7. Runtime hours = available BTUs ÷ effective load
8. Runtime days = runtime hours ÷ operating hours per day
The calculator uses 91,500 BTUs per gallon as the standard propane energy value. Delivery efficiency helps model line losses, regulator performance, or practical system conditions.
Garden work often depends on stable fuel. Propane powers greenhouse heaters, patio burners, weed torches, crop covers, and emergency pump setups. A short runtime can interrupt frost protection, seedling care, and evening maintenance. A tank duration calculator helps you plan fuel before work begins. It also reduces surprise refill trips and rushed shutdowns.
Tank duration depends on more than nominal size. Current fill level matters first. Reserve fuel matters next. Many users never want to drain a cylinder completely. Appliance load also matters. A 35,000 BTU heater and a 100,000 BTU heater use fuel very differently. Duty cycle is just as important. Thermostatic heaters do not burn constantly. Intermittent weed burners also cycle on and off. Seasonal demand can raise consumption because cold air increases heat loss and longer sessions become common.
Gardening conditions change fast. A greenhouse may need overnight heat, but only on cold weeks. A patio nursery can use propane during frost alerts and then sit idle for days. Backup irrigation or generator support can add extra demand during storms. Because of this, a flat estimate is often misleading. A better method combines fill level, reserve, duty cycle, multiple appliances, and daily operating hours. That creates a more practical answer.
This propane tank duration calculator converts pounds to gallons, estimates usable BTUs, and shows runtime in hours, days, and weeks. It also gives a gallons per hour burn rate and an optional usable fuel cost estimate. The graph compares runtime across fill levels using your current settings. That makes refill planning easier. Use the export buttons when you want to keep a record, share a result, or compare fuel scenarios for greenhouse heating and outdoor garden equipment.
Use the appliance input rating from the product label or manual. That value is usually shown as BTU per hour. If several devices share one tank, enter the rating for one unit and increase the appliance count.
Yes. Choose pounds as the input basis. The calculator converts pounds to gallons using the propane density field. The default density is 4.24 pounds per gallon, which is a common planning value.
A reserve helps you avoid planning around a fully empty tank. It creates a safer operating margin, supports timely refills, and reflects real usage habits where users stop before the tank is completely depleted.
Duty cycle is the share of time your appliance actually burns fuel. A heater running half the time has a 50 percent duty cycle. This gives a more realistic duration estimate than assuming nonstop operation.
Yes, often indirectly. Cold weather can raise heating demand and extend run time for greenhouse protection. That is why this calculator includes a seasonal demand factor, which lets you model tougher outdoor conditions.
It is a practical adjustment for line losses, real operating conditions, or conservative planning. If you do not need that adjustment, leave efficiency at 100 percent and the calculator will use the full standard energy value.
Yes. It is especially useful for greenhouse heating because those systems often cycle through the day and night. Enter the heater BTU rating, expected duty cycle, and daily hours to get a stronger runtime estimate.
The graph shows estimated runtime hours at fill levels from 10 percent to 100 percent. It uses your current reserve, load, appliance count, efficiency, and seasonal settings so you can compare refill thresholds quickly.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.