Solar Roof Electric

Solar power, explained simply

Size My System

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How big a solar system would I need?

Answer a few questions for a close estimate of system size, panel count and installed cost. Nothing is submitted anywhere and nothing is stored.

Last reviewed July 2026 · Estimates land within roughly ±15% · Nothing on this page is for sale

Most accurate route: find last year’s total kilowatt-hours on your electric bill and enter it in Step 1. That single number beats every estimate below it. If you don’t have a bill handy, skip to Step 2 and we’ll work it out from your appliances.

Step 1 · Where do you live?

This sets how many hours of usable sun your roof gets. It is the single biggest factor in system size.

Step 2 · Your electric bill most accurate

Look for “kWh” on your bill. If it shows a 12-month total, use that. If it only shows one month, enter that instead and pick which.

Entered a number here? You can skip Step 3 entirely.

Step 3 · No bill handy? Estimate it

Only used if Step 2 is blank. Gas appliances use no electricity, so answering these correctly matters more than you would expect.

Any of these? Tick all that apply.

How this estimate works

No black box. Here is exactly what the calculator does with your answers.

  1. Works out your annual electricity use. If you entered a bill figure it uses that and ignores everything else. Otherwise it adds a base load — lighting, refrigeration, electronics and standby power, scaled to your home size and household — to whichever major appliances you told it run on electricity.
  2. Converts that into system size. Annual kilowatt-hours divided by (peak sun hours × 365 × 0.80). That 0.80 is a real-world derate for wiring losses, heat, dust and inverter inefficiency. Estimates that leave it out come back roughly a fifth too small.
  3. Turns size into panels. Divided by 425 watts per panel, which is typical in 2026. Panels currently range from about 400 to 460 watts.
  4. Applies 2026 pricing. $2.50 to $3.50 per watt installed, which is the normal national range. There is no federal tax credit subtracted, because for buyers it no longer exists.
  5. Sanity-checks your roof. About 20 square feet per panel, so you can see whether the array would physically fit.
Where the ±15% comes from

Shade, roof angle, roof direction, local weather and how a particular installer prices work all move the real number. The band widens further if your roof faces east or west, if trees shade it for part of the day, or if you live somewhere with unusually harsh winters.

This is a starting point for a conversation, not a quote. Use it to judge whether the proposals you receive are in a sensible range — that is what it is genuinely good for.

Why the bill figure beats the estimate

Appliance estimates work from averages. Your actual house has its own habits: how warm you keep it, how often the dryer runs, whether someone is home all day, how old the refrigerator is. Those add up.

Twelve months of real kilowatt-hours captures every one of those without guessing. If you can find that number, the estimate below improves dramatically. Most utilities show a 12-month usage graph in your online account.

Nothing you type here is sent anywhere. The calculation runs entirely in your own browser. No data is collected, stored or transmitted, and there is no form to submit. Figures are national ranges as of the review date and will differ at your address.

Sources

  1. U.S. Energy Information Administration, Residential Energy Consumption Survey — household electricity use.
  2. U.S. Energy Information Administration, How much electricity does an American home use?
  3. Unbound Solar, Peak sun hours by US region.
  4. EnergySage, How many solar panels do I need — panel wattage and sizing.
  5. EnergySage, Solar panel cost — cost per watt.

Appliance figures are rounded typical values for homes that have that appliance running on electricity, not averages across all homes. They are deliberately conservative. Your own bill is always the better input.