Quick answer: Most homes need a 5 kW to 10 kW system. The average US home uses about 10,800 kWh a year (around 900 kWh a month), which needs roughly 7 kW in a sunny state like California. Your own number comes from your annual kWh, not your square footage.
“What size solar system do I need?” sounds like it should have one tidy answer. In practice, the right size follows how much electricity your household uses today and how much it will use over the next decade. This guide gives you lookup tables you can use in two minutes, then shows how a battery, an EV, and NEM 3.0 change the answer.
Solar System Size Chart by Monthly Usage
Find your average monthly kWh on your utility bill, then read across. This chart assumes about 1,500 kWh produced per kW each year, a typical figure for California, Texas, and Florida.
| Monthly use | Annual use | System size needed | Approx. panels (430 W) |
|---|---|---|---|
| 500 kWh | 6,000 kWh | 4.0 kW | 10 |
| 700 kWh | 8,400 kWh | 5.6 kW | 13 |
| 900 kWh | 10,800 kWh | 7.2 kW | 17 |
| 1,000 kWh | 12,000 kWh | 8.0 kW | 19 |
| 1,250 kWh | 15,000 kWh | 10.0 kW | 24 |
Sizes assume 100 percent offset. Panel counts are rounded up. EnergySage uses the same 1.5 production ratio for California.
How to Use This Chart
- Use 12 months of bills, not one month, because summer and winter swing widely.
- Find the row closest to your annual kWh.
- Add any planned loads from the add-on table below.
- Want the full math with your own sun hours? See our step-by-step solar system sizing formula.
- Want to turn kW into a roof layout? Read how many solar panels your home needs.
What Size Solar System Do I Need for My Home Size?
Floor area is a rough guide at best. A frugal family in a large gas-heated home can use less power than a small all-electric home with two EVs. Use this table only as a first guess before you check your bills.
| Home size | Typical annual use | Approx. system size |
|---|---|---|
| 1,000 sq. ft. | 4,710 kWh | 3.1 kW |
| 2,000 sq. ft. | 9,420 kWh | 6.3 kW |
| 2,500 sq. ft. | 11,775 kWh | 7.9 kW |
| 3,000 sq. ft. | 14,130 kWh | 9.4 kW |
Usage figures from EnergySage. System size uses 1,500 kWh per kW.
How Large a Solar System Do I Need by State?
The same home needs a bigger system where the sun is weaker. This table sizes a home that uses 10,800 kWh a year using SunWatts per-kW production data for major cities.
| State (city) | kWh produced per 1 kW | System size for 10,800 kWh |
|---|---|---|
| California (Los Angeles) | 1,708 | 6.3 kW |
| California (Sacramento) | 1,620 | 6.7 kW |
| Texas (Dallas) | 1,552 | 7.0 kW |
| Florida (Orlando) | 1,570 | 6.9 kW |
| Illinois (Chicago) | 1,307 | 8.3 kW |
Source: SunWatts (PVWatts-based, fixed roof mount, 20-degree tilt, south-facing). Real results depend on your roof. For a closer look at these states, see solar system size in Texas, Florida, and Illinois.
Why Illinois Needs a Larger System
Illinois gets fewer peak sun hours and more cloud cover, so each kilowatt produces less. EnergySage shows the same effect: an average home needs about 7.3 kW in California but about 9.9 kW in Massachusetts.
Adjust Your Size for an EV, Heat Pump or Pool
The chart sizes for the home you have today. Panels last 25 years or more, so build in loads you can see coming.
| Added load | Extra annual use | Extra solar (at 1,500 kWh per kW) |
|---|---|---|
| Electric vehicle | about 3,000 kWh | about 2.0 kW |
| Heated swimming pool | about 2,500 kWh | about 1.7 kW |
| Outdoor hot tub | about 3,300 kWh | about 2.2 kW |
| Central air conditioning | about 1,000 kWh | about 0.7 kW |
| Heat pump (replacing gas) | 2,000 to 6,000 kWh | 1.3 to 4.0 kW |
Sources: EnergySage appliance table and Pacific Solar guidance.
Size for Planned Loads, Not “Maybe Someday”
- Include loads with a real timeline, such as an EV in the next 12 to 24 months.
- Skip speculative capacity you may never use.
- Adding panels later means a second permit, a second crew, and often a second inspection.
NEM 3.0 and Batteries: How Big Should You Go?
Under California’s NEM 3.0 net billing, midday exports earn far less than the evening power you buy back. That changes the target offset, not just the cost.
| Setup | Suggested offset of annual use | Why |
|---|---|---|
| Solar only | about 90 to 100 percent | Extra midday power earns very little |
| Solar plus battery | about 100 to 110 percent | Surplus charges the battery for evening use |
Source: Pacific Solar sizing guidance. Your design should confirm the exact target for your rate plan.
How Big a Battery?
Most homes pairing storage with solar look at about 10 to 20 kWh of battery. Size the array and battery together: a large battery on a small array never fills, and a large array with no storage gives away its best hours. Learn more in solar battery storage 101 and net metering, and NEM 3.0 explained.
Does Size Still Affect a Tax Credit?
No, not for purchases. The 30 percent federal residential credit for cash and loan purchases expired on December 31, 2025, so a bigger system no longer earns a bigger credit. Some leases and PPAs still pass through a commercial credit. Confirm details with a tax professional.
Will Your Roof Fit the System?
Sometimes the roof, not the math, sets the ceiling. This table shows the space needed for common sizes using panels about 5.5 by 3 feet.
| System size | Roof area with 400 W panels | Roof area with 450 W panels |
|---|---|---|
| 4 kW | 165 sq. ft. | 149 sq. ft. |
| 6 kW | 248 sq. ft. | 231 sq. ft. |
| 8 kW | 330 sq. ft. | 297 sq. ft. |
| 10 kW | 413 sq. ft. | 380 sq. ft. |
Source: EnergySage. Usable area shrinks after north-facing slopes, vents, chimneys, and fire setbacks.
If Your Roof Is Tight
- Choose higher-wattage panels to reach the same kW in less space.
- Favor south- and west-facing planes.
- Pair a smaller array with a battery to offset more of your bill.
Undersized vs Oversized: What Each Costs You
| Mistake | What happens |
|---|---|
| Undersized | You keep buying expensive grid power and savings shrink |
| Oversized (no battery) | You pay for panels whose surplus earns little under NEM 3.0 |
| Right-sized | Covers current use plus planned additions, with faster payback |
Cost scales with size, so budget matters. See current benchmarks in our guide to solar panel cost in California, and never cut a system so small it barely dents your bill.
How Axia Solar Estimates Your System Size
The chart gives you a starting point. A real estimate uses your address, usage history, and rate plan. Use the solar cost calculator for California or the solar calculator to turn your kWh into a number you can take into every quote.
What You Get With US Power
- Qcells panels sourced factory-direct through US Power
- CSLB-licensed consultants who confirm your size and layout
- A 25-year warranty on every install
- Free estimates for homeowners in California, Texas, Florida, and Illinois
Get Your Number
Ready for firm figures? Get a free solar estimate for your home and compare it with the size you found here.
Frequently Asked Questions
What size solar system do I need for an average home?
The average US home uses about 10,800 kWh a year, which needs roughly 7 kW in a sunny state. Most homes land between 5 kW and 10 kW, so use the chart above with your own annual kWh.
How large a solar system do I need to cover my whole bill?
Divide your annual kWh by the kWh each kilowatt produces where you live, about 1,300 to 1,700. For 10,800 kWh in California, that is about 6.3 to 7.2 kW.
Is 7 kW enough to run a house?
A 7 kW system produces roughly 10,500 kWh a year at 1,500 kWh per kW, which covers an average home. Homes with an EV, a pool, or heavy air conditioning may need 8 kW to 10 kW.
Is a 10 kW solar system too big?
Not for homes that use around 15,000 kWh a year or plan to add an EV or heat pump. For a home under 12,000 kWh with no battery, it is likely oversized.
How big a solar system will I need with an EV?
An EV adds roughly 3,000 kWh a year, or about 2 kW of extra solar in a sunny state. Include it if the purchase is likely within the next one to two years.
Does a battery change the size of the system I need?
It can. With a battery, sizing to about 100 to 110 percent of usage often makes sense, because surplus daytime power gets stored instead of exported cheaply.
Is the 20 percent oversizing rule still a good idea?
Mostly no in California. Under NEM 3.0, extra production without storage earns little, so match your real use plus confirmed near-term loads.
Can my roof limit the size I can install?
Yes. Shading, north-facing slopes, vents, and fire setbacks all reduce usable area. Higher-wattage panels and a battery can help a smaller array do more.