What Size Home Battery Do You Need in 2026?
Most homes need 5–15 kWh of battery. Essentials backup runs 10–20 kWh; whole-home backup 20–40 kWh+. Here’s how to size from usage, critical load and your actual goal — not a sales quote.
Battery size is a load question, not a house-size question. The median U.S. home uses about 29 kWh per day (EIA), but most homes only need 5–15 kWh of storage for bill shifting or essentials backup. Whole-home backup is where the numbers jump.
Size by the decision you’re making
| Goal | Typical battery size | What it covers |
|---|---|---|
| Time-of-use bill shifting | 5–13.5 kWh | Evening loads; 30% of daily use is a common planning share |
| Solar self-consumption | 10–15 kWh | Evening use of daytime surplus; one 13.5 kWh unit fits many homes |
| Essentials backup | 10–20 kWh | Fridge, lights, router, medical equipment; hours to a day |
| Whole-home, 24 hours | 20–40 kWh+ | A/C, heat pump, well pump, EV charging drive the top end |
The sizing formula
Start with the energy you need to carry through the period that matters: usable kWh = average load (kW) × hours you need to cover. Then divide by usable capacity and round up to a standard size:
| Your load | Hours | Raw need | Standard size to plan for |
|---|---|---|---|
| 1.2 kW essentials | 8 hours | 9.6 kWh | 10 kWh |
| 3 kW half-house | 8 hours | 24 kWh | 27 kWh (or two units) |
| 7.5 kW whole-home | 24 hours | 180 kWh | Not practical — use a generator |
That last row is the honest one: batteries are poor at multi-day whole-home coverage. If you need that, a generator or solar-plus-storage with recharging is the right tool. Compare backup options →
Four inputs that change the answer
- Evening consumption. The battery only helps if the energy is used after the sun goes down.
- Critical load. Measure what actually must run in an outage — not the whole panel.
- Solar surplus. Storage can’t soak up more than your evening load can absorb; 30–50% of daily use is a practical planning range.
- Usable capacity. Nameplate kWh is not delivered kWh; reserve capacity, efficiency and degradation shave the number down. Why usable kWh matters →
Enter monthly usage, critical load, outage hours and solar surplus — the calculator returns a size ladder with runtime and one-click ROI.
Sources
- Tesla — How much battery storage do I need? (EIA median usage)
- Solrite Energy — How many kWh of battery to back up a house
- NRG Clean Power — Home battery backup in California (2026)
- Sun Supply — Sizing a solar battery for whole-home backup (2026)
All figures checked November 2026. Ranges are planning estimates, not guarantees.