How many kWh to power a house for a day?
The average US home used about 28.4 kWh a day in 2024 (EIA: 863 kWh a month). Running it on batteries for 24 hours takes about 31.6 kWh of usable battery through a 90% inverter — 4 units of 10 kWh.
How to work it out
- 28.4 kWh a day × 100% × 24 h ÷ 24 = 28.4 kWh of use
- ÷ 90% inverter = 31.6 kWh usable battery → 4 units of 10 kWh
- or 31 batteries (1.024 kWh usable each) · 8 modules (4.096 kWh usable each)
A day of a whole average house is a big ask of a battery. Many backup plans are smaller: keep the fridge, lights, internet and heating controls going, and let the dryer, oven and central air wait for the grid.
Adjust for your project
More options: Share · Inverter eff.
- Battery units
- 4 units
- 12 V 100 Ah LiFePO4 batteries (at 80% usable)
- 31 batteries
- 48 V 100 Ah LiFePO4 modules (at 80% usable)
- 8 modules
- Average load during the outage
- 1,183 W
- Backing up a whole house takes a large battery. Many outage plans cover essentials only — fridge and freezer, lights, internet, the furnace fan or well pump — and let the big heating, cooling and cooking loads wait.
- Battery size covers how long; the inverter’s continuous and surge rating covers what can run at once — a well pump or central air needs a much bigger inverter than lights and a fridge.
Battery needed for longer outages
| Outage to cover | Usable battery needed | Battery units | 48 V 100 Ah LiFePO4 modules (at 80% usable) |
|---|---|---|---|
| 4 | 5.3 kWh | 1 unit | 2 modules |
| 8 | 10.5 kWh | 2 units | 3 modules |
| 12 | 15.8 kWh | 2 units | 4 modules |
| 24 | 31.6 kWh | 4 units | 8 modules |
| 48 | 63.1 kWh | 7 units | 16 modules |
| 72 | 94.7 kWh | 10 units | 24 modules |
What to know about a day of backup
- Your state changes it. EIA’s 2024 averages ran from 495 kWh a month in Hawaii (about 16 kWh a day) to 1,202 in Louisiana (about 40 kWh a day). Your bill beats both.
- Essentials are much smaller. The essentials list on this calculator — fridge, freezer, lights, router, charging and a furnace fan — is about 6.8 kWh a day, or about 7.5 kWh of usable battery for 24 hours: a power station or a few 100 Ah batteries rather than a whole-house system.
- Average power is about 1,183 W. 28.4 kWh over 24 hours averages about 1.2 kW, but peaks are much higher when the AC, oven or well pump runs — size the inverter on those.
- Solar refills it. About 8 kW of panels in a Dallas-like climate makes roughly a day’s average use on an average day; see how many solar panels to run an average house.
Counting in 100 Ah batteries? See how many 100Ah batteries to power a house. With a generator instead: what size generator to run a house. For 48 V modules, a 48V 100Ah battery in kWh shows what each holds.
Different size? Use the full Home Backup Battery Calculator.
What you’ll need
- Plug-in electricity usage monitorBudget price
Plugs in between the wall and a 120 V appliance and shows real watts and kWh over a day — the honest way to fill in a load list, especially for fridges that cycle on and off.
See options on Amazon (opens in a new tab) - 12 V 100 Ah LiFePO4 batteryPremium price
About 1.28 kWh rated in a box roughly the size of a group 24–31 lead-acid battery at around half the weight. Check the BMS discharge limit and whether it can charge below freezing.
See options on Amazon (opens in a new tab)
As an Amazon Associate we earn from qualifying purchases. Links to products are affiliate links — they cost you nothing extra and help keep these calculators free.
Frequently asked questions
How much battery for a fridge, lights and router in an outage?
About 2.6 kWh of usable battery for 24 hours — about what a 3,000 Wh power station delivers, if its inverter handles the fridge’s start.
How many kWh to power a house for 3 days?
About 94.7 kWh of usable battery — 10 units of 10 kWh.
How many kWh to power a house overnight (12 hours)?
About 15.8 kWh at the average rate.
Other common sizes
- How many 100Ah batteries to power a house — 31 × 12 V 100Ah LiFePO4 (8 for essentials)
Sources
- U.S. Energy Information Administration — Electric Sales, Revenue, and Average Price, Table 5A (2024 data, released October 2025) (opens in a new tab) — 2024 average residential customer: 863 kWh a month (about 10,359 kWh a year, 28.4 kWh a day); Louisiana 1,202 kWh a month, Hawaii 495.
- Champion Power Equipment — Generator Wattage Chart (opens in a new tab) — Typical running and starting watts for household, RV and job-site appliances (a manufacturer’s planning chart — your nameplate wins).
- Victron Energy — Lithium Battery Smart manual, technical data (opens in a new tab) — LiFePO4 12.8 V: cycle life 2,500 at 80% DoD, 3,000 at 70%, 5,000 at 50% (to 80% of capacity); 92% round-trip efficiency; 12.8 V 100 Ah: recommended continuous discharge ≤100 A (1C), maximum 200 A; capacity about 20% lower at 0 °C; charge only between +5 °C and +50 °C.
- Victron Energy — Energy Unlimited (book) (opens in a new tab) — Lead-acid charge efficiency 80–95% (85% suggested as a starting value); battery energy efficiency about 75% for full cycles, about 89% in partial state of charge; inverter efficiencies above 90%.
- OSHA Fact Sheet — Using Portable Generators Safely (opens in a new tab) — Never attach a generator to a building’s wiring unless a qualified electrician has installed a transfer switch; 3–4 ft of clear space around the unit.
- U.S. Consumer Product Safety Commission — Portable Generator Hazards (Safety Alert 5123, 2021) (opens in a new tab) — Never run a generator indoors or in a garage, even with doors open; place it outside far from doors, windows and vents; CO alarms; never “backfeed” by plugging into a wall outlet.