List all appliances you want to run on the inverter
Note the wattage of each appliance
Add the wattage of all appliances to get total load in watts
Convert watts to volt-amperes if needed using VA = Watts ÷ Power Factor
Add a safety margin of 20% to 30% for startup surge and future expansion
Check the inverter’s continuous power rating to ensure it exceeds the total calculated load
Check the inverter’s surge power rating to ensure it can handle motor or compressor startup loads
Convert total watts to battery current using Current (A) = Watts ÷ Battery Voltage
Select a battery bank that can supply the required current for the desired backup time
Verify that the inverter input voltage matches the battery bank voltage
Ensure cable size, fuse, and breaker ratings are suitable for the calculated current
Recalculate if any appliance has a high starting load such as a refrigerator, pump, or air conditioner