GreenWattWise LabFree tool
What Size Home Battery Do You Actually Need?
Estimate a sensible battery capacity range based on your household use, solar system and how you expect to use the battery.
Your household
If you only know your annual electricity use, divide it by 365 (e.g. 5,500 kWh/year ≈ 15 kWh/day).
This is often more important for battery sizing than total daily consumption.
Enter the rated DC capacity of your rooftop PV system. Enter 0 if you don't have solar yet.
How much excess solar do you typically export on a good day? (optional)
Refine my estimate
Fill in your household details and press Calculate My Battery Range to see your estimate here.
Ready to make a buying decision?
The Home Battery Buyer Toolkit gives you the complete GreenWattWiseLab decision system, combining the Essential Edition, Battery Decision Calculator and the additional buyer resources included in the Toolkit.
Independent, manufacturer-neutral battery guidance.
Prefer to start smaller?
Start here
Just learning the fundamentals?
Before You Buy a Home Battery — Essential Edition — understand the battery numbers that matter, common sizing mistakes and the questions worth asking before you buy.
Calculation tool
Want the calculation tool on its own?
Home Battery Decision Calculator — explore your own household and battery scenarios and test how different assumptions affect the decision. This free calculator gives you a quick estimate; the Decision Calculator is for deeper scenario exploration.
How this estimate works
1. Estimate how much energy you use when solar isn't producing.
2. Estimate how much solar energy may be available to charge a battery.
3. Use the smaller of those values as the daily energy-shifting opportunity.
4. Convert that into a practical battery capacity range.
Daily shifting opportunity = min(nighttime electricity use, available solar surplus)
Recommended usable capacity ≈ 85–120% of that daily shifting opportunity
kWh tells you how much energy the battery stores. kW tells you how much power it can deliver at one time. This calculator estimates energy capacity, not required inverter power.
This calculator provides an educational estimate, not a final system design. Actual battery sizing depends on interval consumption, solar generation, inverter limits, tariffs, backup requirements, installation constraints and battery specifications.
What Size Home Battery Do I Need? (Full Guide)
The cornerstone guide behind this calculator: consumption, solar production, backup goals, and usable capacity, explained step by step.
Read the Battery Sizing Guide