How to use the generator sizing
Prepare the values for this calculation
Estimate generator nameplate power from connected real load, demand factor and reserve margin entered by the user. Use the formula below to check that it answers your question. Read the input units before transferring figures from a statement, measurement or dataset.
Enter and check each input
- Connected load (kW): enter a value at least 0. Use the unit named in the label or selected above. Do not leave this required field blank.
- Demand factor: enter a value at least 0 and no more than 1. Use the unit named in the label or selected above. Do not leave this required field blank.
- Reserve margin (%): enter a value at least 0 and no more than 500. Use the unit named in the label or selected above. Do not leave this required field blank.
The input table gives a complete example. Keep units and time periods consistent across related fields.
Calculate and resolve any input error
Choose Calculate after entering the values. Changes also update the answer after a short pause. If an error appears, follow its message, correct the field and calculate again. Reset restores the example values.
Interpret the answer
Check Estimated generator size first. With the unchanged example inputs, it is 96 kW. Interpret it using the formula and assumptions on this page.
Compare and keep a useful result
For a controlled comparison, keep every other example input unchanged and change Connected load (kW) from 100 to 110. The resulting Estimated generator size is 105.6 kW. This illustrates the equation’s response to that input, rather than a forecast of real events.
Read the chart’s axis labels and data table. A scenario curve changes one stated input while holding the others fixed; it does not add external observations. Use Download graph to save an available chart as a PNG.
Use Copy result or Download CSV to keep the answer. Share tool shares the page address without placing your input values in the URL. Recheck inputs and assumptions before using the result for a decision.
Generator Sizing formula
Required kW=connected kW×demand factor×(1+reserve).
Inputs and units
| Input | Format / range | Example |
|---|---|---|
| Connected load (kW) | minimum 0 | 100 |
| Demand factor | minimum 0; maximum 1 | 0.8 |
| Reserve margin (%) | minimum 0; maximum 500 | 20 |
Worked example
Using the example inputs above, the estimated generator size is 96 kW.
- Estimated generator size
- 96 kW
Results and assumptions
Planning estimate using user-selected demand and reserve factors; starting kVA, harmonics and manufacturer derating are not included.
Fix an input or unexpected result
Connected load (kW) is required. Enter connected load (kw) using the format and bounds in the input table. Zero and an empty field are different: use zero only if it is allowed and represents your data.
If your answer differs from the example, choose Reset and compare every field, including selected units and options. Check percentage versus decimal entry and whether values describe the same period. Round only the final displayed answer when reproducing the formula.
If a discrepancy remains, report the calculator issue with the page address, non-sensitive example inputs, actual result, expected result and a reference for your calculation.