Generator Runtime Calculator / Propane vs gas

Propane vs Gas Generators: Runtime, Storage & Cost Compared

Dual-fuel generators run on either gasoline or propane, and the right choice depends on how you plan to use it. This guide compares the two fuels on runtime, power output, storage, cold weather, and cost — then shows how to estimate runtime for your own setup.

The short version

• Gasoline gives you more power and more runtime per gallon, and it's easy to find — but it goes stale in months and is awkward to store in quantity.
• Propane stores for years without degrading and burns cleaner, but delivers fewer watts and less runtime per gallon, and small cylinders struggle in deep cold.
• If you already have a dual-fuel generator, the practical answer is often both: gasoline for day-to-day use, propane as the long-storage backup.

Runtime: gasoline wins per gallon, propane wins per tank

Gasoline contains about 114,000 BTU per gallon; propane contains roughly 91,500. A generator therefore burns more propane than gasoline to produce the same electricity — expect roughly 20–25% more fuel volume per hour on propane, all else equal.

The catch is how the fuels are packaged. Gasoline runtime is limited by the generator's tank, commonly 3–8 gallons on portable models. Propane comes in cylinders and tanks of almost any size: a 20 lb cylinder holds only about 4.7 gallons of propane, but a 100 lb cylinder holds about 23.6 gallons, and a household bulk tank far more. A generator plumbed into a large propane tank can run for days — longer than any reasonable gasoline supply — without refueling.

Real example from our verified database: the Westinghouse WGen11500TFc is manufacturer-rated at up to 19 hours at 25% load on its gasoline tank, and about 7 hours at 25% load on a 20 lb propane cylinder. The gasoline figure looks far better — until you connect a larger propane supply.

Power output: expect less on propane

Dual-fuel generators are rated at lower wattage on propane — typically around 5–10% fewer running watts, and a similar reduction in starting watts. A refrigerator or well pump that starts fine on gasoline may trip the overload on propane. Always check the propane ratings, not just the headline gasoline numbers, before planning your load.

Storage: propane's biggest advantage

Gasoline degrades. Without stabilizer it can start going stale within a few months; even stabilized fuel should be rotated within a year or so. Stale gasoline is a leading cause of generators that won't start during an outage. Propane, by contrast, keeps indefinitely in a sound cylinder — it doesn't degrade, varnish, or absorb water. For a generator that sits unused for most of the year, propane removes the fuel-rotation chore entirely.

Cold weather: a real propane limitation

Propane feeds the engine as a vapor boiled off the liquid in the tank. As temperature drops, vapor pressure falls, and a small cylinder may not supply a large generator at full load — especially as the cylinder empties and has less liquid surface to boil from. Gasoline has no equivalent issue. If you expect to run in deep winter cold, use the largest propane tank practical, or plan on gasoline.

Cost and availability

Propane is often cheaper per gallon than gasoline, but the generator burns more of it per hour, and cylinder exchanges carry a convenience premium — so cost per hour of runtime is usually similar or somewhat higher on propane. Gasoline is available at any gas station but is exactly what everyone else is queuing for during an outage; propane suppliers and exchange cages are often less mobbed. Compare local prices per hour of runtime, not per gallon.

Maintenance and engine wear

Propane burns cleaner than gasoline: less carbon buildup, cleaner spark plugs, and no fuel varnish in the carburetor after storage. Gasoline generators that sit with fuel in the carburetor are prone to clogged jets — the classic "won't start after a year in the garage" failure. This is another reason propane suits occasional emergency use.

Which should you choose?

• Choose gasoline if you need maximum watts from a given generator, run in very cold weather, or refuel frequently and easily.
• Choose propane if the generator sits in storage most of the year, you want multi-day runtime from a bulk tank, or you want to avoid fuel rotation and carburetor problems.
• Choose a dual-fuel model if you want both options — most owners end up using gasoline day-to-day and keeping propane as the long-storage reserve.

Estimate your own runtime

The runtime calculator handles both fuels: pick your generator in Find My Generator mode to see manufacturer-verified gasoline and propane figures side by side, or use Quick Estimate with any fuel amount. Not sure what size you need? The generator sizing calculator adds up your appliances, and the generator database lists dual-fuel models with verified specifications for both fuels.

Frequently asked questions