Generator Run Time Calculator
Calculate how long your generator will run on a given fuel tank. Enter fuel capacity, consumption rate, and load for accurate run time estimates.
Formula & How It Works
Run Time (hours) = Fuel Tank Capacity / (Consumption Rate × Load Factor)
Generator fuel consumption is typically rated at 50% load. At lower loads, the generator burns proportionally less fuel. A generator rated at 1.0 gal/hr at 50% load will burn about 0.5 gal/hr at 25% load and 1.5 gal/hr at 100% load. The load factor adjusts consumption based on how hard the generator is working.
Generator Fuel Consumption Reference
| Generator Size | Fuel Type | Tank Size | 50% Load (gal/hr) | Run Time at 50% |
|---|---|---|---|---|
| 2,000W | Gasoline | 1 gal | 0.15 | 6.7 hrs |
| 3,500W | Gasoline | 4 gal | 0.30 | 13.3 hrs |
| 5,000W | Gasoline | 5 gal | 0.50 | 10.0 hrs |
| 7,500W | Gasoline | 8 gal | 0.75 | 10.7 hrs |
| 10,000W | Gasoline | 10 gal | 1.00 | 10.0 hrs |
| 12,000W | Propane | 20 lb (4.7 gal) | 0.95 | 4.9 hrs |
| 15,000W | Propane | 40 lb (9.4 gal) | 1.20 | 7.8 hrs |
| 20,000W | Diesel | 20 gal | 1.40 | 14.3 hrs |
| 22,000W | Natural Gas | Pipeline | 2.50 therms/hr | Unlimited (pipeline) |
Maximizing Generator Run Time
- Run at 50-75% load: Optimal fuel efficiency; idle loads waste fuel
- Use eco-throttle: Inverter generators auto-adjust engine speed to match load
- Maintain the generator: Clean air filters and fresh oil improve fuel efficiency 10-15%
- Stabilize fuel: Add fuel stabilizer for storage; gasoline degrades in 30-60 days
- Propane advantage: Propane stores indefinitely and burns cleaner, but delivers 20-30% less runtime per gallon equivalent
- Diesel efficiency: Diesel generators burn 20-30% less fuel per kW than gasoline equivalents
Frequently Asked Questions
How long will a generator run on a tank of gas?
A typical 5,000W portable generator with a 5-gallon tank runs about 8-10 hours at 50% load. A 2,000W inverter generator with a 1-gallon tank runs 6-8 hours at 25% load with eco-throttle. Larger 10,000W generators with 10-gallon tanks run 8-12 hours at 50% load.
How long will a 20 lb propane tank run a generator?
A 20 lb propane tank (4.7 gallons) typically runs a 7,500W generator for 4-5 hours at 50% load. A 12,000W generator will run about 4-5 hours, while a smaller 3,500W generator can run 8-10 hours. Propane generators consume about 20-30% more fuel per kW than gasoline generators.
How can I make my generator run longer?
Run at 50-75% load for optimal efficiency, use eco-throttle on inverter generators, keep air filters clean, use fresh stabilized fuel, and reduce unnecessary loads. Adding an external fuel tank can extend run time. For standby generators, natural gas provides unlimited runtime via pipeline connection.
How much fuel does a generator use per hour?
Fuel consumption varies by generator size and load. A 5,000W generator burns about 0.5 gal/hr at 50% load. A 10,000W generator burns about 1.0 gal/hr. Diesel generators are 20-30% more fuel efficient. Consumption roughly doubles from 25% to 100% load, so reducing loads significantly extends runtime.
Can I run a generator 24 hours a day?
Portable generators need to shut down every 8-12 hours for oil checks and refueling. Most are rated for 8-12 hour continuous operation. Standby generators are designed for extended operation (24+ hours) with proper maintenance intervals. Always follow the manufacturer's duty cycle recommendations and check oil levels regularly during extended runs.