Generator Fuel Calculator
Factors that Affect Diesel-Powered Generator Fuel Usage
The amount of fuel a generator uses depends on multiple mechanical, operational, and environmental factors. Our calculator’s estimates are approximate and based on recommended use for diesel-powered generators. The following factors can cause variations in fuel consumption:
- Generator Load – Light loads below 30% of capacity can make the engine run inefficiently and waste fuel, while heavy loads close to 70-80% of capacity give the best fuel economy. Overloading increases fuel consumption significantly and risks damaging the unit.
- Generator Size – Larger generators burn more fuel per hour, but they may be more efficient per kWh of electricity produced if properly loaded. However, when a generator is too large for the operating load, a condition called wet stacking can happen. This is when unburned diesel builds up in the generator’s exhaust, causing fuel waste, engine damage, and potential shutdowns.
- Generator Engine Efficiency – Modern diesel engines with electronic fuel injection and turbocharging tend to consume fuel more efficiently than older models.
- Fuel Quality – Low-grade diesel and diesel contaminated with water, microbes, or debris can cause incomplete combustion, leading to higher fuel consumption and more wear on components.
- Operating Conditions – Factors such as high altitudes, extreme hot and cold temperatures, and high humidity can all contribute to increased fuel consumption.
- Maintenance Practices – Generators that are serviced regularly will burn less fuel in general. Dirty air filters, clogged fuel filters, worn injectors, and poor lubrication can all reduce fuel efficiency.
- Operating Time & Start/Stop Cycles – Operating a generator with frequent starts and stops consumes more fuel than running it for long stretches of time at a steady load.
Diesel Generator Fuel Consumption Per Hour Formula
Simple & Easy to Remember Formula
7 gallons = 1 hour @ 100kw
This simple formula leaves out a lot of variables, but it is useful for quick estimates.
Complex but more Accurate Formula
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Find the Actual Load (kW):
Load (kW) = Rated kW × Load Percentage
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Determine the Specific Fuel Consumption (SFC):
Most diesel generators burn between 0.05 and 0.08 gallons per kWh, depending on size and efficiency.
Typical ranges:-
Small portable generator: 0.07–0.09 gal/kWh
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Medium industrial generator: 0.06–0.07 gal/kWh
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Large efficient generator: 0.05–0.06 gal/kWh
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Apply the Formula:
Fuel Consumption (gal/hr) = Load (kW) × SFC (gal/kWh)
Example
A 100 kW generator running at 75% load (75 kW) with an SFC of 0.065 gal/kWh:
75 kW × 0.065 gal/kWh = 4.875 gal/hr
So the generator would use roughly 4.9 gallons of diesel per hour under those conditions.