TL;DR — Is gas or propane cheaper for a generator?
Gasoline often costs less per hour when the two fuels have similar prices per gallon because gasoline contains more energy. But propane can be cheaper if your refill or bulk-delivery price is sufficiently low. I compare actual fuel cost per hour rather than price per gallon alone. If you only use a generator during outages, propane also offers a major storage advantage: properly stored propane fuel does not go stale like gasoline. The winner depends on local prices, generator load, and the model’s consumption ratings.
Is it cheaper to run a generator on gas or propane? In many situations, gasoline wins on fuel consumption, while propane can win on long-term convenience and storage. I wouldn’t make the decision from pump prices alone. I would calculate how many gallons the generator burns for each hour of useful electricity and compare what I actually pay for those gallons. To distinguish fuel energy from useful electricity, see my propane vs. gasoline generator efficiency comparison. For an older unit, I would also consider the 5 signs a propane generator may need replacement when deciding whether continuing repairs makes financial sense.
Here’s how I do that, with sample costs, fuel-energy figures, generator specifications, cylinder runtime estimates, and the tradeoffs that matter during a power outage. Throughout this article, “gas” means gasoline, not natural gas. If noise matters as much as operating cost, I also compare whether propane generators are quieter than gasoline generators.
Gasoline vs. Propane Generator: Quick Comparison
| Comparison | Gasoline | Propane (LPG) |
|---|---|---|
| Energy per U.S. gallon | About 120,214 BTU | About 91,452 BTU |
| Power output on many dual-fuel models | Usually the higher running-watt rating | Often roughly 5–10% lower; check your exact model |
| Fuel storage | Ages and needs proper rotation/storage | Fuel does not degrade in a sealed, sound cylinder |
| Typical fuel supply | Gas can or built-in tank | Portable cylinder or correctly sized bulk tank |
| Fuel pricing | Station price per gallon | Refill, exchange, or delivered price varies widely |
| Best advantage | Strong output and often low fuel cost per useful kWh | Emergency readiness and cleaner fuel handling |
| Important drawback | Gasoline can deteriorate in storage | Small-cylinder exchanges may be expensive per usable gallon |
The energy values above come from the U.S. Energy Information Administration. These are fuel energy inputs, not a promise that any generator converts every BTU to electricity. Actual electrical efficiency depends on the engine, generator, and load.
Why Gasoline Often Costs Less to Run
Gasoline contains more energy per gallon. Using the EIA values, one gallon of propane has about 76% of the heat energy in a gallon of gasoline. Another way to think about it: at equal conversion efficiency, you would need about 1.31 gallons of propane to equal the energy in a gallon of gasoline.
That does not automatically mean a propane generator is 31% more expensive to run. Engine efficiency differs between fuels, and propane may have a lower price per gallon. I use those energy figures as background, then rely on the generator manufacturer’s load-specific fuel consumption when possible.
Real dual-fuel generator power ratings
Consider published specifications for Champion’s 5,500-watt-class dual-fuel model 201505. It is rated at 5,500 running watts on gasoline and 5,000 running watts on propane. That is a 500-watt difference, or about 9.1% of the gasoline running rating. The figures are specific to that model and should not be assumed for every generator.
| Manufacturer specification | On gasoline | On propane |
|---|---|---|
| Starting watts | 6,875 W | 6,250 W |
| Rated running watts | 5,500 W | 5,000 W |
| Reported runtime at 50% rated load | 11 hours | 6.5 hours |
| Fuel container used for runtime | Built-in gasoline tank | Manufacturer’s specified propane cylinder |
Source: Champion Power Equipment, model 201505. Caution: the two runtime tests use different fuel containers and each fuel’s half-rated-load condition; the runtime numbers alone are not a direct gallons-per-hour comparison.
How Much Does a Generator Cost to Run Per Hour?
This is the calculation I recommend before deciding which fuel to buy:
Total fuel cost = hourly cost × hours of operation. Cost per kWh = hourly cost ÷ average electrical output in kW.
Let me use an illustrative scenario, not a claimed national fuel price or a promise about a particular generator. Suppose the same dual-fuel unit, serving roughly the same electrical demand, burns 0.70 gallon of gasoline per hour or 0.90 gallon of propane per hour. Say gasoline is $3.50 per gallon and a propane refill works out to $2.50 per gallon.
| Sample input or result | Gasoline | Propane |
|---|---|---|
| Fuel price (example only) | $3.50/gallon | $2.50/gallon |
| Consumption (assumed) | 0.70 gallon/hour | 0.90 gallon/hour |
| Cost per hour | $2.45 | $2.25 |
| Cost for 8 hours | $19.60 | $18.00 |
| Cost for 24 hours | $58.80 | $54.00 |
| Cost for 72 hours | $176.40 | $162.00 |
| Cost per kWh at constant 3 kW output | $0.82/kWh | $0.75/kWh |
In this example, propane costs $0.20 less per hour, despite burning more gallons. If you pay $3.50 per gallon for both fuels instead, the outcome changes: gasoline remains $2.45 per hour while propane costs $3.15 per hour. That’s why I always ask what the propane refill price is—not just the gasoline pump price.
Important: The 0.70 and 0.90 gallon/hour consumption figures are hypothetical inputs for learning the calculation. Before making a purchase, substitute consumption figures measured at the same electrical output from your generator manual or a reliable test.
At What Propane Price Does It Become Cheaper Than Gasoline?
I like to calculate the break-even point. With the example rates above, the propane price can be no more than $2.72 per gallon (rounded) to match gasoline’s $2.45/hour cost at $3.50/gallon.
Break-even propane price = gasoline hourly cost ÷ propane gallons per hour. Here, $2.45 ÷ 0.90 = about $2.72 per gallon.
| Propane price (illustrative) | Propane hourly cost at 0.90 gal/h | Winner vs. gasoline at $2.45/h |
|---|---|---|
| $2.00/gal | $1.80 | Propane |
| $2.50/gal | $2.25 | Propane |
| $2.72/gal | $2.45 approximately | Roughly tied |
| $3.00/gal | $2.70 | Gasoline |
| $4.00/gal | $3.60 | Gasoline |
This is especially useful if you have access to bulk propane. Delivered propane, refill-station propane, and cylinder exchanges can have very different effective prices. I would never assume that a posted cylinder exchange price represents the same number of gallons as a full 20-pound refill.
How Long Will a 20-Pound Propane Tank Run a Generator?
A nominal 20-pound grill cylinder holds approximately 4.7 gallons of propane when properly filled to its rated propane capacity. At roughly 4.24 pounds per U.S. gallon, 20 pounds corresponds to about 4.7 gallons. Your actual fill can be lower, particularly when using exchanges.
To estimate runtime, divide the usable gallons by the generator’s hourly propane consumption. I would treat these numbers as planning estimates, not guaranteed operating hours.
| Propane consumption | Estimated hours from 4.7 gallons | Approximate fuel used in 8 hours |
|---|---|---|
| 0.4 gal/hour | 11.8 hours | 3.2 gallons |
| 0.6 gal/hour | 7.8 hours | 4.8 gallons |
| 0.8 gal/hour | 5.9 hours | 6.4 gallons |
| 1.0 gal/hour | 4.7 hours | 8.0 gallons |
| 1.2 gal/hour | 3.9 hours | 9.6 gallons |
For a high-demand load, a single 20-pound cylinder may not last an eight-hour outage. Cold weather, tank pressure, regulator sizing, and the cylinder’s ability to vaporize propane also matter. A generator may struggle to draw sufficient vapor even when there is liquid propane left in a small cylinder. I would follow the generator’s minimum cylinder size and regulator instructions rather than improvising a larger supply.
What About a 100-Pound Cylinder or 250-Gallon Tank?
For frequent outages, a larger, manufacturer-approved propane supply can make refueling more convenient. The fuel itself may also be cheaper per gallon when delivered or refilled in larger quantities, although delivery fees and minimum purchase requirements can erase the savings.
| Storage option | Approximate usable propane | Example runtime at 0.9 gal/h |
|---|---|---|
| 20-lb cylinder | 4.7 gal | 5.2 hours |
| 100-lb cylinder | 23.6 gal | 26.2 hours |
| 250-gallon stationary tank at 80% fill | 200 gal | 222 hours |
The storage examples assume a fully rated fill and continuous consumption at the sample rate. The stationary tank’s 80% fill limit allows for liquid expansion. Actual usable volume, reserve, temperature, and vaporization constraints can shorten runtime. A tank’s size is not an assurance that it can provide the flow your generator demands.
Gasoline vs. Propane for Emergency Backup Power
For occasional outages, I lean toward propane storage
If I expect the generator to sit unused for months, fuel freshness matters. Gasoline degrades over time, especially with poor storage conditions, and aging fuel can cause starting and carburetor problems. Fuel stabilizers can help within their instructions, but they do not make gasoline last forever.
Propane does not become stale simply from storage. The cylinder, valves, seals, regulator, and connections still need proper inspection and maintenance. This advantage can offset some extra fuel cost for a backup generator that operates only a few times each year.
For frequent use, I calculate cost per kWh
For a generator running every week or powering a jobsite, a difference of even $0.30 per hour accumulates. I would compare the purchase price, expected annual run hours, maintenance, and delivered fuel costs. Most importantly, I would compare fuel economy at the output I actually need, not at 25% load for one fuel and 50% for the other.
For higher electrical loads, check propane running watts
Dual-fuel units often produce less rated power on propane. For example, if your refrigerator, air conditioner, and other appliances require a combined running load near a model’s propane rating, you may have less headroom for motor-starting surges. I would check both running and starting ratings before buying. A generator that meets the load on gasoline may not meet it on propane.
Hidden Costs That Can Change the Answer
| Cost factor | What I would check | Why it matters |
|---|---|---|
| Generator purchase | Gas-only vs. dual-fuel model price | Upfront difference affects total ownership cost |
| Propane cylinder | Cylinder purchase, recertification, exchange/refill | Adds to propane cost when not already owned |
| Fuel delivery | Minimum quantities and delivery fees | Can change effective propane price per gallon |
| Gasoline storage | Approved containers and fuel rotation | Unused gas has a real cost when replaced |
| Oil and maintenance | Manufacturer’s service interval for both fuels | Propane does not eliminate oil changes or inspections |
| Power output | Usable watts on each fuel | Lower propane output may require a bigger generator |
| Run frequency | Annual operating hours | Even small hourly differences accumulate |
What I would not assume is that propane always makes a generator quieter or maintenance-free. Noise depends on the specific model and operating conditions. Propane avoids gasoline-related carburetor deposits when operated exclusively on LPG, but engine oil, filters, spark plugs, and fuel connections still require attention.
Is a Dual-Fuel Generator Worth It?
If fuel flexibility matters to you, I think a properly sized dual-fuel generator can be a sensible purchase. You can choose gasoline when it is economical and readily available, and propane when stored fuel is the priority. During a widespread outage, having two approved fuel options may help when one supply is difficult to obtain.
The premium is only worthwhile if you will use the flexibility or storage advantage. If you already have a large propane tank, the math may be favorable. If all your propane comes from expensive small-cylinder exchanges, gasoline may remain the lower-cost option for long runs.
How to Reduce Generator Fuel Consumption
- Measure your real load. I would use a wattmeter or the generator’s load display to understand the appliances I’m powering.
- Avoid unnecessary loads. Turn off nonessential resistance heaters and other high-draw equipment when practical.
- Compare the right operating modes. Inverter units can save fuel at light loads, but follow the specific generator’s instructions.
- Maintain the generator. Follow oil, air-filter, spark-plug, and fuel-system service schedules.
- Buy propane by the actual amount received. Compare refill gallons or pounds rather than cylinder labels alone.
- Plan your runtime. Calculate gallons needed before an outage rather than relying on a cylinder that might run empty overnight.
Generator Safety: Both Fuels Produce Carbon Monoxide
Never operate a gasoline or propane generator inside a home, garage, shed, crawlspace, or partially enclosed structure—even with doors or windows open. Both combustion fuels can produce deadly carbon monoxide. I would run a portable generator outdoors, at least 20 feet from the house when feasible, with exhaust directed away from openings, and follow the manufacturer’s instructions. Install working CO alarms indoors.
Do not connect a generator directly to household wiring through an outlet. Use an approved transfer switch or other code-compliant connection installed as required by local rules. Shut down and let a gasoline generator cool before refueling; follow manufacturer instructions for propane cylinder changes and leak checking. See the CDC’s generator carbon monoxide safety guidance.
Frequently Asked Questions
Is propane always cheaper than gasoline for a generator?
No. I compare price per gallon and consumption at the same load. Propane can be cheaper if its price is low enough, but gasoline usually supplies more fuel energy per gallon.
Does a generator use more propane than gasoline?
It commonly uses more gallons of propane for a similar electrical output because propane contains less energy per gallon. The exact difference varies with the generator and operating load.
Does a generator run longer on gas or propane?
There is no universal answer without specifying fuel quantity. A large propane tank can run far longer than a small gasoline tank, while one gallon of gasoline usually contains more energy than one gallon of propane. Compare equal usable fuel quantities or calculate runtime for your actual containers.
Is propane better than gasoline for a backup generator?
For a generator that sits between emergencies, I value propane’s long-term fuel storage. For frequent heavy use, I focus on delivered fuel price, electrical output, and fuel consumption. A dual-fuel unit offers flexibility if your budget allows. If long-term dependability matters more than fuel price alone, see my guide to whether propane generators are reliable and what to expect.
How much does it cost to run a generator for 24 hours?
Multiply hourly fuel use by fuel price, then by 24. At the hypothetical rates used above, that is $58.80 for gasoline or $54.00 for propane. Your actual cost can be much higher or lower, depending on generator size, load, and local fuel price.
My Bottom Line: Which Fuel Would I Choose?
If the priority is the lowest operating cost, I calculate hourly cost using measured fuel use at the same load. Gasoline often wins when gallon prices are close, but a good bulk propane price can turn the comparison around. If the priority is emergency readiness after long storage, I give propane serious consideration. And if I want flexibility during outages, I favor a suitably sized dual-fuel model.
Before you decide, write down your gasoline price, your actual propane refill price, the load you need, and the generator’s gallons-per-hour ratings. That four-number comparison will tell you more than any blanket claim that one fuel is always cheaper.
Technical references: U.S. EIA fuel energy conversion factors · Champion model 201505 specifications · CDC portable generator safety.
Mike is an experienced propane technician with over 15 years of professional experience in the field. He has dedicated his career to helping customers with their propane needs, from installation to maintenance and repair. Together with Jeremy, he co-founded this website to provide useful information and guidance to customers seeking reliable propane services.
