Generator Runtime Calculator
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The Generator Runtime Calculator calculates how many days a generator can support its critical loads during a power outage. This information is an input for characterizing redundant systems in the TRN risk assessment methodology as part of Baseline Development (BD) Action 3. This tool provides two different options for calculating runtime:

  1. If daily consumption (kWh) is known or a reliable estimate is available
  2. If daily fuel consumption is unknown, but generator size (kW) is known

Using either of these options, you will obtain an output establishing the number of days that current redundant generator systems will be able to meet critical loads. This analysis provides a high-level estimate. For users who have done or are planning to do more refined assessments of the runtime capabilities for their redundant systems, those estimates may be more appropriate to use as inputs for the TRN analysis. This tool provides estimates for runtime only for generators using fossil fuels. For other types of electric redundant systems, the user should use other resources to characterize their runtime capabilities.

To see the calculations behind the results, click the “Show Calculations” checkbox. Click “Example” to see an example analysis including entered data and results.

Calculator related questions, suggests, and issues can be submitted here:

Select the fuel type used by your generator. Note that natural gas is not included as a fuel type for generators in this tool. Natural gas generators are connected directly to a natural gas line. Unless a natural gas disruption has also occurred, a natural gas generator will have an "infinite" runtime. However, natural gas generator manufacturers recommend running for no longer than 500 hours at a time so the generator can cool down and any required oil changes or filter replacements can be conducted.

Fuel Type
BTU content of fuel per gallon
BTU per Gallon
Select Method
Daily Consumption
Calculation assumes that generator has sufficient capacity to meet required kW demand
ERROR: Daily consumption must be greater than 0 kWh.
Enter the data below to characterize your generator. Refer to the tool tips next to each question for more information.
Generator Size
ERROR: Generator size must be greater than 0 kW.
Daily Load Factor
ERROR: Load factor must be a value between 0 and 100.
Generator Efficiency
ERROR: Generator efficiency must be a value between 0 and 100%.
WARNING: The generator efficiency you have entered is higher than is typical, please confirm before proceeding.
Daily fuel consumed by generator (BTUs)
BTU per Day
Gallons per day consumed
Gallons per Day
Onsite fuel storage capacity
ERROR: Fuel storage capacity must be greater than 0 gallons.
Days critical load can be met
Is fuel delivery available from offsite and can it arrive before onsite fuel runs out ( days)?
Enter the data below to describe any refueling processes in place to provide additional fuel for your generator during an outage. Refer to the tool tips next to each question for more information.
If refueling is available, will the fuel storage dedicated to the generator be completely refueled?
How many gallons will be supplied?
ERROR: Number of gallons supplied must be greater than 0 gallons.
Additional days provided by a single refueling
Does the refueling recur every days or is it one-time event?
The results below show the calculated runtime for the redundant system described by the inputs to this calculator. The runtime is shown in days and in hours. Use the runtime in hours as an input to characterize your electric redundant system in the TRN Baseline Development Action 3.
Complete the form and address any errors above to view calculated generator runtime.
Longest duration of outage this redundant system could support
The expected runtime is longer than the greatest outage modeled in the TRN. Days
Recurring fuel delivery assumes constant operation
Input for 'Estimated Run Time (hrs)' in the TRN, Baseline Development Action 3