How Generator Fuel Consumption Is Calculated
Generator fuel consumption is primarily determined by three variables: generator size (in kilowatts), the percentage of rated load the generator is currently running, and the fuel type. Most manufacturers publish fuel consumption data at 25%, 50%, and full load — the figures in this calculator are based on industry-standard consumption rates at each load level.
The fundamental formula: Fuel per Hour = Base Rate (per kW) × Generator kW × Load Fraction. For a 5 kW gasoline generator at 50% load: 0.5 gal/kW/hr × 5 kW × 0.5 = 1.25 gallons per hour.
Fuel Consumption by Type
Gasoline
The most common generator fuel in residential applications. A typical portable gasoline generator consumes 0.5–0.6 gallons per kilowatt per hour at full load. Gasoline has a shelf life of 3–6 months without stabiliser (12 months with stabiliser) — critical for emergency preparedness stockpiling. Ethanol-blended fuels (E10, E15) have shorter shelf lives and can cause fuel system corrosion in generators stored for extended periods.
Diesel
Diesel generators are 20–30% more fuel-efficient than gasoline equivalents. A 5 kW diesel generator at 50% load uses approximately 0.9–1.0 gallons per hour versus 1.25 for gasoline. Diesel stores for up to 12 months with fuel stabiliser and is generally more energy-dense. Most standby generators above 20 kW use diesel. Running diesel generators below 30% rated load for extended periods can cause "wet stacking" — incomplete combustion that deposits unburned fuel in the exhaust system.
Propane (LP Gas)
Propane generators are popular for their indefinite fuel storage life — propane does not degrade with age like liquid fuels. However, propane has lower energy density than gasoline or diesel, requiring approximately 20–25% more fuel volume for equivalent output. Propane generators are well-suited for homes with existing LP supply (rural properties, areas with unreliable fuel supply chains) and are popular for standby whole-house generator systems.
Natural Gas
Natural gas generators connect directly to the utility supply line, eliminating fuel storage entirely. This makes them the most convenient option for extended outages — as long as the gas supply remains intact. Natural gas generators are primarily used as permanent standby systems. Consumption is measured in cubic feet (CF) or cubic meters (m³) per hour, and consumption costs vary significantly by utility rate and region.
Planning for Extended Power Outages
The key insight for emergency preparedness planning is that continuous operation is rarely necessary. Running a generator 6–8 hours per day for essential functions (refrigerator cycling, phone charging, medical equipment, lighting) consumes far less fuel than continuous operation. For a 3-day outage at 8 hours/day with a 5,000-watt generator at 50% load using gasoline: 1.25 gal/hr × 8 hrs × 3 days = 30 gallons — a realistic stockpile for most households.
- Refrigerator: 150–200 watts average running load; can be cycled on/off every few hours
- Sump pump: 750–1,250 watts when running (intermittent)
- Window AC unit: 1,000–1,500 watts (significant load — avoid running continuously)
- LED lighting (6 fixtures): 60–120 watts total
- Phone/laptop charging: 100–200 watts total
- Total essential load estimate: 600–800 watts average (approximately 15–20% of a 5 kW generator)