How Many Solar Panels Do I Need for My House?

Work out your panel count in four steps

The example home uses 1,000 kWh a month. Swap in your own numbers as you go. The shaded box in each step shows the example result.

1. Add up a year of electricity use

   Find “kWh used” on each bill, or the 12-month usage chart most utilities print on the bill or show in your online account. Add 12 months. One month alone misleads, because air conditioning and electric heat swing with the seasons.

   1,000 kWh × 12 months12,000 kWh a year

2. Divide by what 1 kW of panels makes where you live

   This is the production per kW, in kWh a year. EcoGen’s national figure is 1,424.6, the average of NREL PVWatts estimates for the 50 states and D.C. Use your state’s figure from the state table, or run your address in PVWatts for 1 kW.

   12,000 ÷ 1,424.68.4 kW system

3. Divide by the panel size

   Panel size is printed in watts. Panels of 430 to 440 W were the most common size quoted on the EnergySage marketplace in the first half of 2026. Write 440 W as 0.44 kW. Round up, so the system covers the whole year.

   8.42 ÷ 0.44 = 19.120 panels

4. Check that they fit on your roof

   A 440 W panel such as the Qcells Q.TRON is about 67.8 by 44.6 inches, or 21 square feet (Qcells datasheet). Multiply, then leave room for fire-code walkways and edges (see roof space).

   20 × 21 sq ftAbout 420 sq ft of open roof

The 20 panels make an 8.8 kW system that should produce about 12,500 kWh a year at the national figure, a little more than the home uses. An installer’s design should land close to your own result. If a quote is far off, ask which production figure and panel size it used.

Solar panels needed by monthly electricity use

Find your average monthly use from your bills. The table uses the national 1,424.6 kWh per kW and 440 W panels, and rounds up. In a sunnier or cloudier state, adjust with the state table.

The U.S. average is EIA’s 865 kWh a month per home customer in 2024 (EIA). The cost guide prices each system size; its size table rounds to the nearest panel, so a 7.95 kW system shows as 18 panels there.

How many solar panels you need in each state

The same home needs fewer panels where the sun is stronger. Each row shows what 1 kW of panels makes in a year in that state, and the system a home using 1,000 kWh a month would need. For 500 kWh a month, halve the system size; for 1,500 kWh, multiply it by 1.5. Then divide by 0.44 for the panel count.

Production figures are the yearly output of 1 kW of panels in each state’s sunlight, from NREL PVWatts version 8, as used in EcoGen’s state solar payback guides. Each is a single location’s figure for the state (New York’s, for example, is New York City; Albany makes less). Your roof’s direction, tilt and shade change them, so a PVWatts run for your own address is the better input.

Solar panels by home size: 1,500, 2,000 and 3,000 sq ft

Floor area is a weak guide on its own, because heating fuel, air conditioning and household size matter more. If you don’t have your bills yet, this is the best rough start: the average electricity use for each home size in EIA’s national home energy survey, sized at the national production figure.

Source: EIA Residential Energy Consumption Survey 2020, Table CE2.1, average electricity per household, converted at 3,412 Btu per kWh. These averages mix apartments with houses and homes heated with gas with those heated by electricity. A 2,000 sq ft home with a heat pump and an electric car can need many more panels than the same home with gas heat.

What raises or lowers your panel count

Roof direction and tilt

South-facing roofs make the most power in the U.S. In NREL’s PVWatts model for a 6 kW system on a 20-degree roof in Atlanta, east- and west-facing panels made about 87% to 88% of what south-facing panels made, and north-facing about 72%.

Shade

Trees, chimneys and nearby buildings cut output. If shade costs 15% of production, the 12,000 kWh home needs 23 panels instead of 20. Ask for the shade report behind any production estimate.

An electric car

An electric vehicle (EV) that uses 27 kWh per 100 miles, the example the U.S. Department of Energy uses, needs about 3,240 kWh for 12,000 miles a year, before charging losses. Charged at home, that adds about 5 panels at national sunshine (20 become 25 for the example home). Check your car’s rating on its window sticker or at fueleconomy.gov.

A heat pump, pool pump or new appliances

Switching heating from gas or oil to a heat pump moves that energy onto your electric bill, mostly in winter when panels make the least. Ask the installer or HVAC contractor for an estimate of the new yearly kWh and add it before sizing. Planned loads are cheaper to add now than as a second installation later.

Utility rules on size and exports

Your utility decides what extra power is worth and sometimes how big you may build. In New Jersey, net metering applies only if the system is not bigger than the power you used over a past 12 months, and leftover credit at year end is paid at the lower wholesale rate (N.J.A.C. 14:8-4.3; see New Jersey net metering). In PG&E’s California net billing tariff, a home can be designed to produce up to 150% of its last 12 months of use if it signs an attestation that new electric loads, such as an EV, are coming within a year (PG&E Schedule NBT). Where exports earn little, building past your own use rarely pays. See how net metering works.

Your main electrical panel

A common electrical-code limit, the “120% rule,” says the main breaker plus the solar circuit (counted at 125% of the inverter’s output current) may not exceed 120% of the panel’s busbar rating, with the solar breaker at the opposite end from the main. On a 200-amp panel with a 200-amp main breaker, that leaves room for a 40-amp solar breaker, enough for an inverter output of about 7.7 kW. A bigger system may need a main panel upgrade or a different connection, so ask whether that work is in the quote.

Will the panels fit on your roof?

Count only the open, sunny parts of the roof. Each 440 W panel needs about 21 square feet, plus small gaps. Vents, skylights, chimneys and dormers take space. Fire codes add walkways: the 2018 International Residential Code calls for two 36-inch paths, on separate roof faces, from the lowest roof edge to the ridge, and a clear strip of 18 inches on both sides of the ridge when panels cover up to a third of the roof (36 inches when they cover more) (2018 IRC R324.6, quoted by the City of Boise). Your city may use a different edition.

Do batteries or going off-grid change the count?

A battery does not change the yearly math for a home that stays on the grid. It stores daytime power for the evening or an outage, which matters most where exports earn little. Going fully off-grid is a different design: the panels must cover your worst winter weeks, not the yearly average, and the batteries must carry you through cloudy days. That takes many more panels and a large battery bank.

Questions about how many solar panels you need