Generator Fuel Consumption Guide
Last updated:
Fact-checked by Marcus Hayes, Master Electrician (License #CA-EL-89241), 15 years generator installation experience.
Fuel consumption is the biggest ongoing cost of generator ownership. A 7,500W generator running for 3 days during an outage can burn $150 to $250 in fuel. Understanding how much fuel your generator uses — and which fuel type is cheapest — helps you budget and prepare. This guide covers gasoline, propane, and natural gas consumption rates.
Key Takeaways
- A 3,500W inverter burns 0.25-0.35 gal/hr at 25% load; a 7,500W generator burns 0.5-0.8 gal/hr at 50% load.
- Inverter generators use 20-40% less fuel than conventional generators at partial loads.
- Gasoline is cheapest per hour but goes stale in 30 days; propane costs 10-20% more but stores indefinitely.
- Natural gas (standby only) costs $1-2/hour and provides unlimited runtime — no fuel storage needed.
- A 20lb propane tank lasts 3-4 hours at 50% load on a 7,500W generator; 10-14 hours at 25% load on a 3,500W inverter.
Fuel consumption by generator size
A 2,000W inverter burns 0.15-0.25 gal/hr at 25% load. A 3,500W inverter burns 0.25-0.35 gal/hr. A 7,500W
open-frame burns 0.5-0.8 gal/hr at 50% load. A 12,000W generator burns 0.8-1.2 gal/hr at 50% load.
Inverter generators are 20-40% more fuel-efficient than conventional generators at partial loads
because they throttle the engine to match demand.
| Generator Size | Load | Gas (gal/hr) | Propane (gal/hr) | Cost/hr (gas) |
|---|---|---|---|---|
| 2,000W inverter | 25% | 0.15-0.25 | 0.18-0.28 | $0.53-$0.88 |
| 3,500W inverter | 25% | 0.25-0.35 | 0.28-0.40 | $0.88-$1.23 |
| 7,500W open-frame | 50% | 0.50-0.80 | 0.55-0.90 | $1.75-$2.80 |
| 12,000W open-frame | 50% | 0.80-1.20 | 0.90-1.35 | $2.80-$4.20 |
| 22kW standby (NG) | 100% | N/A | 2.4 gal/hr | $1.50-$2.00 (NG) |
Gas costs based on $3.50/gallon. Propane costs based on $3.00/gallon. Natural gas costs based on $1.50/therm. Actual consumption varies by model, altitude, and temperature.
Gasoline vs propane vs natural gas
Gasoline is cheapest per hour but goes stale in 30 days and requires stabilizer for storage. Propane
costs 10-20% more per hour but stores indefinitely, burns cleaner, and never needs stabilizer. Natural
gas (standby generators only) costs $1-2/hour and provides unlimited runtime from a utility line —
no fuel storage, no refueling, no shelf life concerns. For emergency preparedness, propane is the
best choice. For convenience, natural gas wins.
Frequently Asked Questions
How much fuel does a generator use per hour?
A 3,500W inverter generator burns 0.25 to 0.35 gallons of gasoline per hour at 25% load. A 7,500W open-frame generator burns 0.5 to 0.8 gallons per hour at 50% load. A 12,000W generator burns 0.8 to 1.2 gallons per hour at 50% load. Inverter generators use 20-40% less fuel than conventional generators at partial loads.
How much does it cost to run a generator per hour?
At $3.50/gallon for gasoline, a 3,500W inverter costs $0.88 to $1.23 per hour at 25% load. A 7,500W generator costs $1.75 to $2.80 per hour. A 12,000W generator costs $2.80 to $4.20 per hour. Propane costs slightly more per hour but stores indefinitely. Natural gas (standby only) costs $1-2/hour.
How long will a generator run on a gallon of gas?
A 3,500W inverter generator runs 3 to 4 hours per gallon at 25% load. A 7,500W generator runs 1.25 to 2 hours per gallon at 50% load. A 12,000W generator runs 0.8 to 1.25 hours per gallon at 50% load. Smaller inverter generators are significantly more fuel-efficient.
Is propane or gasoline cheaper for a generator?
Gasoline is cheaper per hour of runtime. Propane costs about 10-20% more per hour but stores indefinitely (gasoline goes stale in 30 days). For emergency preparedness, propane is the better choice because you can store it for years without stabilizer. For frequent use, gasoline is cheaper.
How much propane does a generator use per hour?
A 7,500W dual-fuel generator uses 1.1 to 1.5 gallons of propane per hour at 50% load. A 20lb propane tank (4.7 gallons) lasts 3 to 4 hours at 50% load. A 20lb tank on a 3,500W inverter at 25% load lasts 10 to 14 hours. Propane produces about 10% less wattage than gasoline.