How Long Will My Generator Run?

Understanding Generator Runtime

Generator runtime is determined by the relationship between how much fuel your generator can hold and how quickly it burns that fuel. Fuel consumption rate is directly tied to the load you're placing on the generator — the more watts you draw, the faster it burns fuel.

Most portable generator specifications include a runtime rating like “up to 10 hours at 50% load.” This figure is useful for comparison shopping, but in real-world use, your load will vary. Our calculator lets you input your actual load wattage so you get a realistic estimate, not a best-case marketing figure.

The 80% Load Rule and Runtime

The generator sizing guideline of running at 80% maximum capacity also improves fuel efficiency. A generator running at 75% load produces more usable power per gallon burned than one running at 30% or 100%. If you find yourself running a large generator at very low load for long periods, you'd actually save money and fuel by switching to a smaller, properly-sized unit.

Extending Runtime: Practical Tips

• Use LED lighting throughout. Switching 10 incandescent bulbs (600W) to LEDs (100W) saves 500W — adding meaningful runtime.
• Cycle refrigerators and freezers. Refrigerators only need power intermittently. Running your generator 8 hours on / 8 hours off keeps food safe while cutting fuel use in half.
• External fuel tanks. Many generators accept external tank hookups via a fuel shutoff valve, effectively doubling or tripling your runtime without carrying the generator.
• Propane for long outages. 100-lb propane tanks (23.6 gallons equivalent) can run a mid-size generator for 2–3 days continuously. Much safer and easier to store than equivalent gasoline.