Generator Fuel Cost Calculator

A generator fuel cost calculation converts an expected run into three operating numbers: Fuel used, Fuel cost, and Cost per hour. These numbers support generator run planning, temporary-power budgeting, load-review decisions, and comparisons between operating scenarios.

The calculation does not size a generator, determine branch-circuit or feeder ampacity, verify voltage drop, select conductor AWG or kcmil, establish raceway fill, or approve a fuel-system installation. Those electrical and field decisions require separate load data, equipment documentation, installation details, and applicable AHJ requirements.

Generator Operating Cost

Generator electrical output and fuel consumption are related operationally, but the fuel-cost result is not an electrical sizing value. A generator can have the required kW or kVA capacity for a connected load while still creating an unacceptable operating cost for a long outage, test run, temporary installation, or remote-power schedule.

Use the result when comparing expected runtime scenarios, such as:

• Daily standby-generator exercise periods
• Temporary power during construction or service work
• Planned outage coverage
• Portable generator operation for a branch circuit or small distribution setup
• Operating-cost review before selecting between available generators

For electrical planning, the fuel-cost screen can be reviewed beside generator output capacity, connected load, starting current, motor inrush, feeder loading, voltage-drop performance, and available fuel supply. It does not replace any of those calculations.

Calculation Inputs

Input	Unit	Use
Fuel burn rate	gal/h	The average generator fuel consumption rate
Runtime	h	The expected operating hours
Fuel price	$/gal	The price paid for each gallon of fuel

Fuel burn rate must be entered as an average value in gallons per hour. The result follows the entered rate directly. If actual fuel consumption varies with electrical load, use a burn rate that represents the expected operating condition rather than treating a single rate as valid for every load level.

Runtime is the total operating time in hours. For multiple runs, enter the combined expected hours when a single total-cost estimate is needed.

Fuel price is entered in dollars per gallon. Keep the fuel-price unit aligned with the burn-rate unit: a gal/h input requires a $/gal fuel price.

Fuel Cost Formula

The calculator applies the following arithmetic:

\(\displaystyle \text{Fuel used} = \text{Fuel burn rate} \times \text{Runtime}\)

\(\displaystyle \text{Fuel cost} = \text{Fuel used} \times \text{Fuel price}\)

\(\displaystyle \text{Cost per hour} = \frac{\text{Fuel cost}}{\text{Runtime}}\)

When runtime is greater than zero, the cost-per-hour result also equals:

\(\displaystyle \text{Cost per hour} = \text{Fuel burn rate} \times \text{Fuel price}\)

Runtime increases total gallons and total fuel expense, while the cost per hour remains tied to the entered Fuel burn rate and Fuel price.

Calculation Example

Enter the following values:

Field	Entered value
Fuel burn rate	1.8 gal/h
Runtime	10 h
Fuel price	$4.25/gal

Calculate fuel use:

\(\displaystyle 1.8\ \text{gal/h} \times 10\ \text{h} = \text{18 gal}\)

Calculate fuel cost:

\(\displaystyle 18\ \text{gal} \times $4.25/\text{gal} = \text{$76.50}\)

Calculate hourly cost:

\(\displaystyle $76.50 \div 10\ \text{h} = $7.65/h\)

The resulting values are:

Result	Value
Fuel used	18 gal
Fuel cost	$76.50
Cost per hour	$7.65/h

A 10-hour generator run at the entered average fuel burn rate requires 18 gallons and produces an estimated fuel expense of $76.50.

Field Verification

Verify the entered Fuel burn rate against the expected operating condition. Generator fuel consumption can change as electrical demand changes, including changes in connected load, cycling equipment, motor starting events, and the operating profile of the load.

For a field decision, separately verify:

• Generator output rating against the calculated load.
• Starting and running requirements for motors and other utilization equipment.
• Branch-circuit, feeder, conductor ampacity, overcurrent protection, and voltage-drop requirements.
• Available fuel quantity and the intended operating duration.
• Manufacturer instructions, site conditions, and AHJ requirements for the generator and fuel system.

The calculator estimates fuel consumption cost from the values entered; it does not select equipment or approve the electrical installation or fuel-system design.