Calculator
Backup power calculator
Add the loads you want to keep running, adjust the numbers to match your appliances, and choose how long to plan for. The estimate updates as you type, runs entirely in your browser, and is saved only on this device.
1. Choose a planning duration
2. Add loads
Wattage varies widely between models. The defaults are rounded starting points, not measurements. Check the label on the appliance (often called the nameplate) or its manual, and replace the defaults whenever you can.
Custom load
3. Adjust your loads
Duty cycle is the share of time an appliance actually draws power while it is in use. A refrigerator compressor that runs about one third of the time has a duty cycle near 33%. A modem that is always on is 100%.