How Big a Home Battery Do You Need?
Enter your usage, what you want to keep running in an outage, and whether you have solar — get a kWh recommendation grounded in your actual profile, not a sales quote.
Sizing for backup, solar shifting or both Standard size ladder with runtime per size One click to run the full ROI on your size
1 Your home profile
Household usage
kWh/mo
kWh/day
Backup goal — what keeps running in an outage
kW
h
Solar
I have (or will have) solar panels
A battery can store your daytime surplus for the evening
2 Your recommendation
—
Calculating… Adjust inputs to see results instantly.
What drives your number
Inverter power ≥
—
to carry your critical load
Raw need
—
before rounding to a standard size
Sizing only — not a quote. Ready for the money question? Run the ROI on this size →
Standard size ladder for your profile
typical installed cost ≈ 944 USD/kWh (US reference, converted)| Size | Est. installed cost | Backup runtime | Covers one outage? | Stores your solar surplus |
|---|
Runtime = size ÷ your critical load. Cost scales linearly at the reference $/kWh — actual quotes vary by brand and installer.
How this calculator works (methodology & assumptions)
Backup driver = critical load (kW) × outage hours you want to cover
Solar driver = min(daily surplus, 35% of daily household use)
Load-shift driver = 30% of daily household use
Raw need = max(active drivers) → round UP to 5 / 10 / 13.5 / 20 / 27 kWh
Inverter power = smallest standard ≥ your critical load
Solar driver = min(daily surplus, 35% of daily household use)
Load-shift driver = 30% of daily household use
Raw need = max(active drivers) → round UP to 5 / 10 / 13.5 / 20 / 27 kWh
Inverter power = smallest standard ≥ your critical load
- Drivers are conservative planning heuristics, not simulations — the goal is the right size class, not a decimal.
- Solar driver (35%): a battery can't absorb unlimited surplus — reuse is limited by how much load you have in the evening.
- Load-shift driver (30%): typical share of daily usage that moves through storage under time-of-use rates.
- Costs use the average installed $/kWh of the batteries tracked in this site (US reference price, 2026-11-06).
- Nameplate ≈ usable: the ladder assumes typical usable capacity; batteries that reserve 5–10% for longevity deliver slightly less — round up if you need guaranteed runtime.
- After sizing, run the ROI calculator to see payback for that size.