How long will a 500 gallon propane tank run a generator?
A 500 gallon tank is filled to 80%, so it holds about 400 gallons of propane. A home standby generator burns roughly 2 to 3 gallons an hour, which is 5.6 to 8.3 days of non-stop running. Enter your own tank, gauge reading and burn rate below.
Runtime by tank size and burn rate
Each tank is filled to 80%. The 2 and 3 gal/h columns are the range Ferrellgas gives. The other two are Generac's published figures for its 22 kW home standby unit (model G0070420): 2.53 gal/h at 50% load and 3.71 gal/h at 100% load.
| Tank | Gallons | 2.00 gal/h | 2.53 gal/h | 3.00 gal/h | 3.71 gal/h |
|---|---|---|---|---|---|
| 250 gal | 200 | 100 h (4.2 d) | 79 h (3.3 d) | 67 h (2.8 d) | 54 h (2.2 d) |
| 500 gal | 400 | 200 h (8.3 d) | 158 h (6.6 d) | 133 h (5.6 d) | 108 h (4.5 d) |
| 1,000 gal | 800 | 400 h (16.7 d) | 316 h (13.2 d) | 267 h (11.1 d) | 216 h (9.0 d) |
Neither source lists 25% or 75% load, and I have no manufacturer figure for them, so those rows are left out. If your spec sheet has them, type the number into the form.
The arithmetic
500 gal × 80% = 400 gal
400 gal ÷ 3 gal/h = 133.3 h = 5.6 days
400 gal ÷ 2 gal/h = 200 h = 8.3 days
Ferrellgas says "a 500-gallon tank that only powers a home's propane generator can last 5-6 days". At 3 gal/h the sum above gives 5.6, so the two agree at the top of the burn range.
Planning a long outage
A delivery truck may not reach you during a storm, so it helps to pick a gauge level you treat as empty. If you count the bottom 20% as off limits, a full 500 gallon tank has 300 usable gallons, which is 100 hours at 3 gal/h. The reserve line is my suggestion. Suppliers don't set it.
The house furnace, water heater and range draw from the same tank, so the generator never has all of it. The tank percentage for each size is on the 500 gallon propane tank chart, and the 1000 gallon propane tank chart covers the larger tank.
Related pages
A portable unit on a grill cylinder is a different sum: see a generator on a 20 lb propane tank. The house's own use is on how much propane a house uses per month, and what size propane tank do I need compares sizes.