A typical portable generator runs 6–12 hours on 5 gallons of gasoline at 50% load. The exact runtime depends on the generator size, load level, and engine efficiency. A small 2,000W inverter generator stretches 5 gallons to roughly 20+ hours at 25% load, while a large 10,000W conventional generator burns through 5 gallons in about 4 hours at 75% load.
Here is the complete runtime chart for every common generator size, followed by fuel-saving strategies that can extend your 5 gallons by 30–50%.
Runtime Chart: 5 Gallons of Gasoline
Inverter vs. Conventional: Inverter generators use significantly less fuel than conventional generators at the same wattage because their engines adjust speed based on load. A 2,200W inverter at 25% load sips fuel at 0.12 gal/hr, while a 3,500W conventional generator at 25% load still burns 0.30 gal/hr — even though both are producing similar wattage.
How to Calculate Runtime for Any Generator
The formula is simple:
Runtime (hours) = Fuel Tank Size (gallons) ÷ Fuel Consumption Rate (gallons per hour)
The key variable is fuel consumption rate, which depends on the generator's load. Most manufacturers publish fuel consumption at 25%, 50%, and 100% load in their spec sheets.
If you only know the fuel consumption at 50% load (the most commonly published figure), you can estimate other loads. At 25% load, fuel consumption is roughly 55–65% of the 50% load rate. At 75% load, consumption is roughly 130–140% of the 50% rate. At 100% load, consumption is roughly 160–175% of the 50% rate.
Example Calculation — Honda EU2200i: The Honda EU2200i has a 0.95-gallon tank and consumes 0.12 gal/hr at 25% load (eco-throttle mode). With 5 gallons of gas: 5 ÷ 0.12 = 41.7 hours of runtime at 25% load. At 50% load (0.24 gal/hr): 5 ÷ 0.24 = 20.8 hours. That is enough to keep a fridge and lights running for almost an entire day on 5 gallons.
Example Calculation — Champion 7500W: The Champion 7500W consumes about 0.80 gal/hr at 50% load. With 5 gallons: 5 ÷ 0.80 = 6.25 hours at 50% load. At 25% load: approximately 0.50 gal/hr, giving 5 ÷ 0.50 = 10 hours. Running a fridge, freezer, and some lights at 25% load stretches your fuel much further.
Example Calculation — Large 10,000W Portable: At 50% load, a typical 10,000W generator burns about 1.10 gal/hr. With 5 gallons: 5 ÷ 1.10 = 4.5 hours. That is barely one evening. At this consumption rate, you need 26+ gallons for a 24-hour outage — more than four 5-gallon gas cans.
Runtime for Other Fuel Quantities
You might not have exactly 5 gallons. Here is the runtime for common fuel amounts using a 5,500W generator at 50% load (0.60 gal/hr).
How Much Gas to Store for Emergencies
How much gasoline you should keep on hand depends on how long you expect outages to last and what load you plan to run.
Gasoline has a shelf life of 3–6 months without stabilizer. Store fuel in approved containers (UL-listed fuel cans), in a cool, ventilated area, away from the house and any ignition sources. Add fuel stabilizer (STA-BIL or similar) at every fill and rotate your supply every 3–6 months. Never store more than 25 gallons of gasoline at a residential property — check your local fire code for exact limits.
Generator Runtime Calculator
7 Ways to Make 5 Gallons Last Longer
1. Run at the Lowest Load Possible
Cut unnecessary loads. Do you really need the TV, the toaster, and every light in the house? Every 100W you eliminate saves fuel. A 7,500W generator at 25% load uses 37% less fuel per hour than at 50% load.
2. Use an Inverter Generator
If you are buying new, an inverter generator's variable-speed engine burns dramatically less fuel at low loads. At 25% load, a 2,200W inverter uses 0.12 gal/hr vs. 0.30 gal/hr for a 3,500W conventional — running 2.5x longer on the same fuel.
3. Cycle Appliances Instead of Running Everything at Once
Run the refrigerator for 1 hour, then turn it off for 2 hours (a well-sealed fridge stays cold for 4–6 hours with the door closed). Run the sump pump on demand, not continuously. This lets you operate at a lower average load.
4. Pre-Cool Your Home Before the Outage
If a storm is forecasted, set your AC to 68–70°F before the power goes out. Your home will stay comfortable for hours without running the AC, saving the most fuel-hungry appliance for later.
5. Switch to LED Lights
If you haven't already, LED bulbs use 80% less electricity than incandescent. Lighting your entire home with LEDs adds only 50–100W of load vs. 500–1,000W with old bulbs.
6. Keep the Generator Well-Maintained
A clean air filter, fresh oil, and new spark plugs improve combustion efficiency by 5–10%. A dirty air filter alone can increase fuel consumption by 10–15%.
7. Use Propane Instead of Gasoline
If you have a dual-fuel generator, propane burns at a slightly lower rate for the energy produced and is available in pre-filled tanks without needing a gas station. Twenty-pound BBQ tanks are available at most hardware stores even during outages.
Real-World Fuel Savings Example: A homeowner in Louisiana used a Champion 5,500W generator during a 24-hour outage. At first, they ran everything at once (50% load = 0.60 gal/hr = 14.4 gallons/day). After cycling appliances and cutting unnecessary loads, they reduced average load to 25% (0.40 gal/hr = 9.6 gallons/day). Fuel savings: 4.8 gallons in 24 hours, or about $15.
Key Takeaways:
- A 5,500W generator runs 8–12 hours on 5 gallons at 50% load.
- A 2,200W inverter runs 20+ hours on 5 gallons at low load — best fuel economy.
- Large generators (10,000W+) burn through 5 gallons in 3.5–5 hours.
- Inverter generators use 30–50% less fuel than conventional generators at the same power output.
- Cut load to 25% by cycling appliances — this can nearly double your runtime.
- Store gasoline with stabilizer and rotate every 3–6 months.
- For 24-hour outages, budget 6–30 gallons depending on your generator size and load.
Frequently Asked Questions
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