Residential Calculators
Battery Size Calculator
Battery sizing has two separate constraints: energy (kWh — how long it lasts) and power (kW — whether it can actually start your appliances). Pick the loads you want to keep running, and we'll size for both.
Your location
Enter your ZIP and we'll pull in your climate zone, solar resource, utility, current electricity rate, TOU availability, and battery incentives automatically.
Enter a 5-digit ZIP to auto-fill everything below.
Your household electricity use
This doesn't directly size your backup — that's driven by the specific loads you pick below — but it tells you how your critical loads compare to your overall usage.
We'll convert this to kWh using your ZIP-derived rate above (or the national average until you enter a ZIP).
Enter your usage above to see how your critical loads compare.
What should stay on during an outage?
Check everything you want backed up. Each item uses a sourced running-watts / startup-watts / duty-cycle default — see the assumptions panel below for exact figures and sources.
Heating & cooling system
Heating and cooling are usually the largest single loads in a home — and the reason a "big enough kWh" battery can still fail to start your air conditioner. The "Central AC" and "Heat pump" checkboxes above pull their wattage from what you select here.
Defaulted to 3 tons (typical for a US home) — edit if you know your actual system size.
For multiple units, enter the combined (aggregate) system size.
Desired backup duration
One of the most important sizing variables. Longer duration scales your energy (kWh) requirement roughly linearly.
Load breakdown
| Load | Running W | Startup W | Daily kWh |
|---|
Recommended battery stack
Assumptions in this estimate
- Sizing reserve margin12.5% (midpoint of a 10–15% range)
- Usable capacity / round-trip loss95%
- Surge conventionContinuous load + single largest motor startup
- Multi-unit power scalingAssumed linear per unit (approximation)
Wattage, duty-cycle, and runtime defaults come from EnergySage, Generac, Honda, and manufacturer datasheets — see each load's tooltip for its specific source. Actual draw varies by appliance model, age, and efficiency. This is a planning estimate, not an engineering design — for panel-level circuit backup or code compliance, work with a licensed electrician.
Enter your ZIP above to see your area's solar resource and how much it could extend your backup between recharges.
Solar + Battery CalculatorEnter your ZIP above to see whether time-of-use rates are available from your utility.
TOU Battery Savings CalculatorEnter your ZIP above to see typical virtual power plant (VPP) enrollment earnings in your area.
VPP Earnings Calculator