Generator Runtime and Fuel Calculator
Geographic Scope: This page covers NewJersey state-level regulations, licensing requirements, and service standards.
Knowing how long a generator will run at a given load helps with fuel planning during
outages and job-site scheduling. This calculator estimates fuel consumption and runtime
based on generator capacity, actual load, and fuel type.
Generator Specifications
Generator Rated Capacity
kW
Actual Load
kW
Fuel Type
Gasoline
Diesel
Propane (LP)
Natural Gas
Tank / Supply Size
gallons
Calculate
Estimated Runtime
Actual consumption varies with altitude, temperature, load fluctuation,
and generator efficiency. Diesel generators are typically 20–30% more fuel-efficient than
gasoline at equivalent loads. Always maintain a fuel reserve for safety.
Fuel Consumption Rates
Generator fuel consumption is primarily determined by load, not rated capacity. A generator
running at 50% load uses significantly less fuel than one at 75% or full load:
| Fuel Type | Consumption at 50% Load | Consumption at 75% Load | Energy Content |
|---|---|---|---|
| Gasoline | ~0.075 gal/kWh | ~0.09 gal/kWh | 33.7 kWh/gal |
| Diesel | ~0.055 gal/kWh | ~0.07 gal/kWh | 40.7 kWh/gal |
| Propane | ~0.10 gal/kWh | ~0.12 gal/kWh | 27.0 kWh/gal |
| Natural Gas | ~10 ft³/kWh | ~12 ft³/kWh | ~0.293 kWh/100 ft³ |
Frequently Asked Questions
How long will a 10kW generator run on 8 gallons of gas?
At 50% load (5 kW), a gasoline generator consumes roughly 0.375 gallons per hour,
giving about 21 hours of runtime. At 75% load (7.5 kW), consumption rises to roughly
0.68 gal/hr, giving about 12 hours. The calculator above provides a precise estimate.
Is it bad to run a generator at full load?
Sustained operation above 75% of rated capacity increases fuel consumption, accelerates
wear, and reduces engine life. Most manufacturers recommend running at 50–75% of rated
capacity for optimal efficiency and longevity.
References
- 2017 National Electrical Code (NEC) as adopted by the Arizona Department of Fire, Building and Life
- 2017 National Electrical Code as adopted by the Tennessee Department of Commerce and Insurance, Divi
- 2020 National Electrical Code (NEC) as adopted by the Pennsylvania Department of Labor & Industr
- 10 CFR Part 431 — Energy Efficiency Program for Certain Commercial and Industrial Equipment (eCFR)
- 2020 New York State Uniform Fire Prevention and Building Code
- 2017 edition per the Arizona Administrative Code (R4-36-101)
- 2020 NEC as referenced by the Georgia Department of Community Affairs (DCA)
- 2022 Lawrence Berkeley National Laboratory report on U.S. Data Center Energy Use