Home Battery Calculator

Right-size your home battery

Answer 5 quick questions and we'll match you with the best battery systems for your home and goals.

Question 1 of 50% complete

What's your main goal?

This helps us focus on what matters most to you.

How to size a home battery

Battery size (kWh) = daily energy to back up × days of backup ÷ 0.85. The 0.85 allows for the share of rated capacity you cannot or should not use, and for losses converting stored power back to household current.

Essentials for 12 hours (fridge, lights, internet, phone charging, about 5 kWh a day): 5 × 0.5 ÷ 0.85 ≈ 3 kWh. Our sizer rounds anything under 5 kWh up to 5, the smallest practical home system.
Essentials plus heating or cooling for a day (about 15 kWh): 15 × 1 ÷ 0.85 ≈ 18 kWh, or two 13.5 kWh batteries.
Whole home for three days (about 30 kWh a day, close to the US average of 28.4 kWh): 30 × 3 ÷ 0.85 ≈ 106 kWh — usually only practical with solar to recharge during the outage.

Check your own daily use on your utility bill: divide the month's kWh by the days in the billing period. Average use ranges from 495 kWh a month in Hawaii to 1,202 kWh in Louisiana; see your state's figures.

Power matters as well as energy. Capacity (kWh) decides how long a battery lasts; its continuous power rating (kW) decides how many appliances can run at once. A central air conditioner or well pump can need more power than a single battery supplies, so ask the installer to check motor starting loads.

Average daily electricity use by state

Average household daily electricity use and Powerwall hours by state
State	kWh per day	Hours per 13.5 kWh
Louisiana	39.5	8
Mississippi	38.0	9
Tennessee	37.9	9
Alabama	37.6	9
Florida	36.3	9
Texas	36.0	9
Oklahoma	35.5	9
Arizona	35.3	9
Georgia	35.3	9
South Carolina	34.5	9
Arkansas	34.5	9
Kentucky	34.4	9
Virginia	33.9	10
North Dakota	33.8	10
West Virginia	33.8	10
North Carolina	33.4	10
Missouri	32.9	10
South Dakota	32.7	10
Nebraska	31.4	10
Washington	31.4	10
Idaho	31.0	10
Nevada	30.6	11
Maryland	30.5	11
Delaware	29.9	11
Indiana	29.6	11
Oregon	29.0	11
Kansas	28.8	11
Wyoming	28.4	11
Montana	28.0	12
Ohio	27.8	12
Iowa	27.4	12
Pennsylvania	26.9	12
Utah	25.5	13
Minnesota	23.4	14
Connecticut	22.8	14
Illinois	22.8	14
Colorado	22.2	15
New Jersey	21.8	15
New Mexico	21.5	15
Wisconsin	21.2	15
District of Columbia	21.0	15
New Hampshire	20.4	16
Michigan	20.3	16
Alaska	19.0	17
Vermont	18.9	17
New York	18.8	17
Massachusetts	18.7	17
Rhode Island	18.6	17
Maine	18.1	18
California	16.5	20
Hawaii	16.3	20

Frequently asked questions

How many kWh battery do I need to power my house?

Multiply the power you want to back up per day by the number of days, then divide by about 0.85 because not all of a battery's rated capacity is usable in practice. The average US home used about 28.4 kWh a day in 2024 (EIA), so a full day of normal use needs roughly 34 kWh of battery. Backing up only essentials such as the fridge, lights and internet takes far less.

How long will a 13.5 kWh battery power a house?

A 13.5 kWh battery, the capacity of one Tesla Powerwall 3, covers about 11 hours of average US household use. Turning off big loads like central air conditioning, electric heat, an electric dryer or EV charging stretches it much further.

Do I need solar to have a home battery?

No. A battery can charge from the grid and supply backup during outages, or shift power from cheap to expensive hours on a time-of-use rate. With solar, it can also store daytime output and recharge during a long outage, which a grid-only battery cannot.

Is there a tax credit for home batteries in 2026?

Not for homeowners buying one. The IRS says the 30% Residential Clean Energy Credit is not allowed for expenditures made after 31 December 2025. Some states and utilities offer storage rebates or pay batteries to support the grid; check DSIRE for your state.

Product specifications and prices in the sizer are copied from manufacturers' US websites and dated on our guides; installed costs are averages. Confirm them with the seller and installer. See our disclaimer.

Sources

U.S. Energy Information Administration, 2024 Average Monthly Bill- Residential — 2024 (annual)
Tesla Powerwall 3 datasheet — 13.5 kWh energy capacity, 11.5 kW continuous power
IRS: FAQs on the modification of sections 25C, 25D and others (FS-2025-05) — 25D ends for expenditures after 31 December 2025