Generator Size Calculator
Estimate the appropriate generator size for residential and portable power needs based on your appliances. The tool c...
What Generator Size Calculator does
Generator Sizer is a free online calculator that helps homeowners estimate the appropriate generator size for residential and portable power needs. By factoring in both running watts and starting (surge) watts of common household devices, the tool determines the wattage capacity required for a specific setup. Users add their planned appliances, and the calculator accounts for the higher surge power needed when motors, compressors, and other inductive loads start up, providing guidance on generator selection before purchase.
How to use the Generator Sizer Generator Size Calculator
- 1
Add the appliances you plan to power using the tool's editable published wattage list
- 2
Set the headroom margin percentage and daily run hours to refine the estimate
- 3
Input your fuel tank size in gallons to calculate daily fuel costs
- 4
Click 'Size my generator' to receive recommendations on generator class and inverter size if needed
- 5
Review the total continuous AC load, heaviest load type, and suggested generator classes displayed alongside popular Amazon options
Best for
Homeowners and DIY enthusiasts planning a portable or standby generator purchase who want to understand their specific wattage requirements before buying.
Limitations
- Results are based on published typical wattages that are editable by users, so accuracy depends on correct appliance input
- The tool provides estimates and does not account for all real-world variables such as simultaneous startup of all listed devices
- No unit switching available; all calculations use watts, gallons, and hours as the default units
Generator Size Calculator FAQ
- Can I use this calculator for a whole-house standby generator?
- The tool is designed for residential and portable power needs; for whole-house standby systems, users should list the backup circuits they want to power, and the calculator will help size a matching transfer switch and generator class.
- What if my appliance isn't in the list?
- Published wattages are editable, so you can adjust the running wattage to match your specific device's nameplate rating for more accurate sizing.
- Does the calculator account for starting surge watts?
- Yes, the tool factors in startup surge requirements for motors, compressors, and other inductive loads, offering load type options such as resistive, motor, and compressor to reflect the higher power draw at startup.
- How do I size an inverter instead of a generator?
- A separate inverter sizing section is available where you input battery capacity, system voltage, AC load watts, and battery chemistry to calculate estimated runtime based on depth-of-discharge and inverter losses.