How Many Solar Panels Do I Need, and How Many Fit on My Roof?

The average Texas home uses about 1,094 kWh of electricity a month, and needs around 22 solar panels (a system of about 9 kW) to cover all of it. Your number could be as low as 10 panels or as high as 50, depending on how much power you use, which panels you buy, and how much sun your roof gets.

This guide gives you a formula you can do on a phone calculator, a chart to check your answer, and a simple way to see whether that many panels will actually fit on your roof.

The simple formula

1. Find your yearly use. Add up 12 months of "kWh used" from your bills, or multiply one month by 12. Using a full year matters in Texas, because summer and winter bills can differ a lot.
2. Divide by 1,460 to get the system size in kW. That's roughly how many kWh one kW of panels produces in a year in Texas, assuming about 5 peak sun hours a day and normal system losses.
3. Multiply by 1,000 and divide by your panel's wattage to get the number of panels. Most new residential panels are 400 to 450 W. Round up.

Example: 1,094 kWh × 12 = 13,128 kWh a year. 13,128 ÷ 1,460 = 9.0 kW. 9,000 ÷ 410 = 21.9, so 22 panels.

Prefer not to do the math? Our solar system size calculator does it for you using your city's sunlight, and the solar roof panel calculator checks what fits on your roof.

Panels needed by monthly kWh

Looking at a specific size? See our cost guides for 5 kW, 6 kW, 8 kW and 10 kW systems.

What changes your number

• Where you live. West Texas gets more sun than the Gulf Coast. A home in El Paso or Lubbock needs fewer panels than the same home in Houston, where humidity and clouds cut production. Peak sun hours across Texas range from roughly 4.5 on the coast to around 6 in the far west.
• Panel wattage. Higher-wattage panels mean fewer panels for the same output. Going from 400 W to 450 W panels cuts the count by about 11%.
• How much you want to offset. You don't have to cover 100% of your bill. More on that below.
• Future changes. Planning to buy an EV, add a pool or switch to electric heat? Add that load now. An EV driven 40 miles a day adds roughly 350 kWh a month, or about 7 more panels.
• Roof direction and shade. East- and west-facing panels make less than south-facing ones, and shade cuts output fast.

How many solar panels fit on my roof?

A typical residential panel is about 65 to 67 inches tall and 39 to 41 inches wide, or roughly 18 sq ft. With spacing for racking, plan on about 19 sq ft per panel.

The catch is that not all of your roof is usable. Fire codes require clear pathways along the ridge and edges, and you'll lose space around vents, chimneys and skylights. North-facing sections usually aren't worth covering. On a standard gable roof, only about 35 to 55% of the total roof area is typically good for panels.

Quick roof estimate:

1. Take your home's footprint in square feet (for a one-story home, about the same as its living area).
2. Multiply by about 1.15 to account for roof pitch and overhangs. That's your rough total roof area.
3. Multiply by 0.4 for the usable, sun-facing portion.
4. Divide by 19 to get the number of panels that will likely fit.

Example: a one-story 2,000 sq ft home: 2,000 × 1.15 × 0.4 ÷ 19 = about 48 panels could fit, plenty for most families. A two-story home with the same living area has about half the roof, so roughly 24 panels, which is tighter. For a more precise estimate for your address, use our solar roof panel calculator.

Roof direction and shade

If most of your usable roof faces east or west, add about 15% more panels to make the same amount of power. In Texas, west-facing panels have a hidden bonus: they produce more in the late afternoon, right when air conditioning use peaks.

Shade is a bigger deal than direction. A single tree shading part of an array can cut output noticeably, especially on systems without microinverters or optimizers. Learn more about how inverters handle shade.

Texas examples

Small home in San Antonio, 750 kWh a month

750 × 12 ÷ 1,460 = 6.2 kW. With 410 W panels: 16 panels, about 300 sq ft of roof. Fits easily on most one-story homes.

Family home in Fort Worth, 1,400 kWh a month

1,400 × 12 ÷ 1,460 = 11.5 kW. With 430 W panels: 27 panels, about 510 sq ft of roof. If the best roof faces west, plan on about 32 panels.

Large home near Houston, 2,200 kWh a month, adding an EV

(2,200 + 350) × 12 ÷ 1,460 = 21 kW. With 430 W panels: 49 panels, about 930 sq ft. A two-story house this size may not have enough good roof, so a ground mount or a partial offset could make more sense.

Should you offset 100%?

Not always. In Texas, most retail electricity plans pay less for the solar power you send back to the grid than they charge for power you buy. That means panels that mostly export at midday earn less than panels whose power you use yourself.

Many Texas homeowners get the best payback by sizing for 70 to 90% of their annual use, especially on plans with low buyback rates. Others in cities with strong buyback programs, like Austin Energy or CPS Energy territory, can justify a full 100%. Check your utility's rules in our Texas net metering guide, then test different sizes in the Texas solar calculator.

Bottom line

Take your yearly kWh, divide by 1,460, multiply by 1,000 and divide by your panel wattage. For the average Texas home, that's about 22 panels. Then check that your roof has roughly 19 sq ft of sunny, usable space for each one. If it's tight, higher-wattage panels or a partial offset will get you most of the savings with fewer panels.