Home Battery Sizing Calculator
Size home battery for outage backup.
Result
Formula
Calculation logicFrequently asked questions
What size home battery for outages?
Cover critical loads only: fridge, lights, internet, and medical. Most homes need 5 to 15 kWh for overnight essentials.
kW vs kWh, which matters?
kWh is how long; kW is how much at once. Motors and microwaves set the kW floor near 3 to 5 kW.
Can batteries run AC?
Central AC needs 3 to 5 kW continuous plus surge. Most single batteries cannot start it without soft-start kits.
How does solar change sizing?
Daytime solar recharges the battery, so overnight-only sizing works. Without solar, size for the full outage.
Related calculators
Calculator
Battery Capacity Calculator
Size battery capacity (kWh) for a backup need.
Open calculatorCalculator
Battery Runtime Calculator
Estimate how long a battery powers a load.
Open calculatorCalculator
EV Charging Cost Calculator
Compare home charging cost against gasoline.
Open calculatorCalculator
EV Charging Time Calculator
Estimate EV charging time from battery and charger power.
Open calculatorWorkspace
Every result shows its math: your inputs, the formula, the numbers.
Save this calculation to return to the inputs, result, and report from your private workspace.
Sign in or create an account to save this calculation.