What size solar system do I need for my house?

Divide your annual electricity usage in kWh by your area's production per kW per year (roughly 1,000 to 1,300 kWh per kW in cloudier regions, 1,500 to 1,900 in the Southwest). A home using 10,800 kWh a year in a 1,450 kWh-per-kW area needs about 7.4 kW to cover 100 percent of usage. Square footage of the house is not the driver; usage is.

How many solar panels is that?

Divide system size in watts by the panel wattage. At 400 watts per panel, a 7.4 kW system is about 19 panels, occupying very roughly 330 square feet of panel area before fire setbacks and spacing. Higher-wattage panels reduce the count and the roof area needed.

Should I size my solar system to cover 100 percent of my usage?

Not always. Where utilities pay much less for exported power than they charge for retail, production beyond what you can use or store earns little, and a system sized at 70 to 90 percent of usage can produce better economics. Where exports earn close to retail, 100 percent sizing is more attractive. Planned changes like an EV or heat pump argue for sizing up.

How do I find my annual kWh usage?

Add the kWh figure from 12 consecutive monthly utility bills, or pull a 12-month usage history from your utility's online account, most utilities show it as a chart or download. For scale, the EIA reports the average U.S. residential customer purchased 10,791 kWh in 2022, but your own number is the one that matters.

What Size Solar System Do You Need?

Not what size house you have; how much electricity you actually use. This calculator turns 12 months of usage into a system size, a panel count, and an approximate roof footprint, with every assumption on a slider you control rather than buried in fine print.

Your annual electricity use (kWh)

Add up 12 months from your utility bills or online account. For scale, the average U.S. residential customer bought 10,791 kWh in 2022 per the EIA.

Share of your usage to cover: 100%

100 percent aims to produce as much as you use over a year. Above 100 rarely pays where exports earn less than retail; below 100 can suit tight roofs or budgets.

Production per kW per year: 1,450 kWh

Varies with sun and shading: roughly 1,000 to 1,300 in cloudier regions, 1,500 to 1,900 in the Southwest. For a location-specific figure, model your address in NREL's free PVWatts tool.

Panel wattage: 400 W

Most residential panels sold today are in the 400 watt range; your quote will say exactly.

Estimated system size

0 kW

Panels needed (at 400 W)0

Approximate panel footprint0 sq ft

Estimated year-1 production0 kWh

Share of your usage covered0%

Footprint counts the panels alone, assuming a typical residential panel of about 17.6 square feet; real layouts need more roof than that for fire setbacks, obstructions, and spacing, and not every roof face produces equally. Estimates only, based on your inputs; an installer's shading and structural analysis, or NREL's PVWatts model for your address, will refine them. General information, not financial or engineering advice.

How the sizing math works

System size in kilowatts equals the annual energy you want to produce divided by how much one kilowatt of panels yields per year where you live. The yield number does the heavy lifting: the same 10,800 kWh target needs about a 9 kW system in a 1,200 kWh-per-kW climate but only about 7 kW in a 1,550 kWh-per-kW one. For a location-specific yield, model your actual address in NREL's PVWatts calculator, the free federal tool installers themselves use for first-pass estimates, then bring that number back to the slider above.

Why 100 percent offset is not automatically the goal

Sizing to cover all of your usage makes clean sense where exported power earns close to retail. Where it earns a fraction of retail, and in much of the country now it does, kilowatt-hours you cannot use or store are your least valuable ones, and a somewhat smaller system often has better economics. That trade-off is exactly what our payback calculator models; use this page for the size, that page for the money, and check your utility's actual export policy on our utility pages.

Reasons to size up anyway

An EV in your future. Charging at home adds thousands of kWh a year, and adding panels later costs more per panel than adding them now.
Electrification plans. A heat pump or induction range shifts gas usage onto the meter this calculator sizes against.
A battery. Storage soaks up midday surplus that would otherwise export at low value, making extra capacity worth more. Our battery guide covers the pairing.

What the roof decides

The footprint figure above counts panel area only. Real installations lose usable roof to fire setbacks, vents, and shading, and faces that point north or sit under trees produce meaningfully less, which is why two neighbors with identical usage can need different systems. An installer's site survey settles it; our guide to choosing a solar installer covers how to vet the people doing the measuring.

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Adjust the height if you'd like; it's responsive and works on mobile.

Frequently asked questions

What size solar system do I need for a 2,000 square foot house?

Square footage is the wrong input; electricity usage is what matters, and two identical houses can use wildly different amounts. Pull 12 months of kWh from your utility bills and use the calculator above. If you only have a monthly average, multiply by 12.

How many panels do most homes end up with?

It follows from usage and climate. A home near the national-average 10,791 kWh per year (EIA, 2022) in a moderate climate lands somewhere around 17 to 22 panels at 400 watts each, but the range across real homes is wide. The calculator shows your number.

Is a bigger system always better?

No. Beyond what you can use, store, or export at a decent rate, extra capacity earns little. Where export rates are low, right-sizing beats max-sizing; run the economics in the payback calculator before deciding.

How accurate is this?

It is a planning estimate driven entirely by your inputs. The production yield varies with roof orientation, tilt, and shading, which is why we point you to NREL's PVWatts for a location-specific figure and why an installer's shading analysis is the final word.

Have your size? Get quotes that match it.

Walking into quotes knowing your target size and panel count changes the conversation. Compare installers and check their proposals against your own numbers.

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General information only, not financial or engineering advice. Production estimates vary with location, roof characteristics, and equipment. Sources: EIA: average U.S. residential electricity use; NREL PVWatts.