Understanding the true cost of running a generator helps you budget for emergency preparedness, compare the economics of different generator sizes, and make informed decisions about when to run the generator versus conserving fuel. The math is straightforward once you know the key variables.
The Variables That Determine Running Cost
- Generator fuel consumption rate (gallons per hour at a given load)
- Current fuel price (gasoline, propane, or natural gas)
- Load level (how much of the generator capacity you are using)
- Hours of operation
Fuel Consumption by Generator Size
| Generator Size | At 25% Load | At 50% Load | At 75% Load |
|---|---|---|---|
| 2,000W inverter | 0.10 gal/hr | 0.15 gal/hr | 0.20 gal/hr |
| 3,500W inverter | 0.13 gal/hr | 0.22 gal/hr | 0.31 gal/hr |
| 5,500W conventional | 0.35 gal/hr | 0.47 gal/hr | 0.60 gal/hr |
| 8,500W conventional | 0.50 gal/hr | 0.72 gal/hr | 0.95 gal/hr |
| 10,000W conventional | 0.60 gal/hr | 0.88 gal/hr | 1.15 gal/hr |
Calculating Hourly Running Cost
The formula is simple:
Hourly Cost = Fuel Consumption Rate (gal/hr) × Fuel Price ($/gal)
Example: 8,500W Generator at 50% Load
- Fuel consumption: 0.72 gallons per hour
- Gasoline price: $3.50 per gallon
- Hourly running cost: 0.72 × $3.50 = $2.52 per hour
- Daily cost (24 hours): $60.48
- Weekly cost: $423
Inverter vs Conventional: The Cost Difference
At 50% load, an inverter generator consumes significantly less fuel than a conventional generator of similar peak wattage. This is because inverter generators throttle down the engine at partial loads rather than running at fixed speed.
Example: 3,500W Inverter vs 5,500W Conventional at the Same Load
- Inverter at 50% load (1,750W actual): 0.22 gal/hr × $3.50 = $0.77/hour
- Conventional at 32% load (same 1,750W actual): 0.40 gal/hr × $3.50 = $1.40/hour
- Inverter savings: $0.63 per hour, or $15 per day of continuous use
Over a week-long outage, that difference amounts to over $100 in fuel savings — a meaningful contribution toward the inverter generator price premium.
Propane Cost Comparison
Propane burns less efficiently in generators than gasoline — a propane-powered generator produces approximately 10–15% less output and consumes more propane by volume for equivalent power. At current propane prices, running costs on propane are typically 15–25% higher than gasoline per kilowatt-hour generated.
However, propane stores indefinitely, which means no fuel waste from degradation and no emergency price gouging from limited gasoline supply after a storm.
Natural Gas: The Cheapest Fuel for Standby Generators
Whole house standby generators running on natural gas have the lowest running costs of any generator type. Natural gas is priced in therms or cubic feet, and the energy equivalent cost is typically 40–60% less than gasoline per kilowatt-hour generated — depending on your local utility rates and current gas prices.
A 20kW natural gas standby generator running at 50% load costs approximately $1.50–$2.50 per hour in fuel — significantly less than the $3.00–$4.50 per hour for a comparable portable gasoline generator.
Total Cost of Ownership
Running cost is only part of the generator economics. Include these factors in a complete cost analysis:
- Purchase price and installation cost
- Annual maintenance: oil, filters, spark plug — approximately $50–$150 per year
- Fuel storage costs: approved containers, stabilizer
- Transfer switch installation if not already in place
- Insurance considerations for standby generators (may increase home value)
Is a Generator Cost-Effective?
For most homeowners in outage-prone areas, the calculation is straightforward. A single extended outage costs: spoiled refrigerator and freezer food ($200–$500), hotel nights ($100–$200 per night), restaurant meals, and lost productivity. A reliable generator prevents all of these losses. Across its 10–15 year lifespan, a well-maintained generator represents excellent value for emergency preparedness.