How to size a generator
Add up what you will run, allow for the surge when motors start, keep some margin. That is the whole method.
Three steps
List what you will run
Write down every tool, appliance or light that must run at the same time. Check the nameplate for watts, or for volts and amps (watts = volts x amps).
Add the starting surge
Motors and compressors draw several times their running power for a moment when they start. Count the largest single surge on top of the total running load.
Keep headroom
Do not run a generator at its limit. Leave a margin of roughly a quarter so it runs cooler and handles changes.
Quick load calculator
Typical values for common appliances. Your equipment may differ: check the nameplate. This is a rough guide; the final size is confirmed in your quote.
Watts, kW and kVA
1 kW is 1,000 watts. Large generators are often rated in kVA. Multiply kVA by the power factor (commonly 0.8) to get kW. A 100 kVA generator at 0.8 delivers about 80 kW.
See the size chart for how our five classes map to typical loads, and single-phase and three-phase power if your equipment needs three-phase.
Sizing questions
What if I am not sure of my load?
Send the quote form with a list of the equipment or a photo of the panel and nameplates. We recommend a class.
Is it bad to rent a generator that is too big?
A generator that is far too large for a small load can run inefficiently. Match the size to the load, with headroom.
Tell us what you need
We reply by email with a quote.