How Many Solar Panels Do I Need to Power My House?

Most homes need somewhere between 15 and 25 modern solar panels to cover their electricity use. The exact number comes down to three things: how much power you use, how much sun you get, and how powerful your panels are.

Here’s how to work it out.

The 3 inputs that decide your panel count

Your annual electricity use (kWh). Check a year of utility bills. The average US home uses around 10,800 kWh/year (~900 kWh/month).
Your local sun hours. This is peak sun hours per day — roughly 4 in cloudier northern states, 6+ in the Southwest.
Panel wattage. Modern residential panels are usually 380–430 W. We’ll use 400 W.

The formula

System size (kW)  = Annual kWh ÷ (Sun hours × 365 × 0.86)
Number of panels  = System size (kW) × 1000 ÷ Panel watts

The 0.86 is a performance ratio — real systems lose some energy to inverters, wiring, heat and dust.

A worked example

Say you use 10,800 kWh/year in a location with 4.5 sun hours/day:

System size = 10,800 ÷ (4.5 × 365 × 0.86) ≈ 7.6 kW
Panels = 7,600 ÷ 400 ≈ 19 panels

In sunny Arizona (6.5 sun hours) the same home would need only about 13 panels. Sunlight matters a lot.

Skip the math — the Solar Panel Size Calculator does this instantly from your usage and state.

Should you size for 100% of your bill?

Not always. Consider:

Net metering rules. If your utility pays full retail for exports, offsetting 100% makes sense. If it pays less, slightly undersizing can improve returns.
Future usage. Planning an EV or heat pump? Size up now.
Roof space. Your roof may cap the count regardless of ideal size.

Next steps

Once you know your panel count, estimate the cost and payback with the Solar Savings Calculator, and read how much solar panels cost for pricing context.

Estimates for education only. A site assessment from a licensed installer will refine roof-specific factors like shading and orientation.