Home Battery Size Calculator
Estimate the battery energy capacity needed to support essential loads for a chosen backup duration.
Home Battery Size Calculator
How the estimate works
Nominal battery capacity ≈ Required backup energy ÷ (usable depth × efficiency)
Backup design also requires a power calculation in kW. A battery can have enough energy capacity in kWh but still be unable to start or support high-power loads such as central air conditioning, electric resistance heat or large pumps.
Primary sources
Frequently asked questions
Is kWh the only battery-sizing number that matters?
No. kWh measures energy capacity; kW measures power. Both must match the loads you plan to run.
Should I back up the whole house?
Not necessarily. Essential-load backup can reduce required battery capacity and inverter power.
Why include depth of discharge and efficiency?
Not all nominal battery energy is practically delivered to loads, so usable-energy assumptions should be included.
Planning estimate only. Local tariffs, equipment performance, installation requirements and incentives can materially change results.