Solar & Renewables

How Many Solar Panels Do I Need?

Enter your electricity usage and location — get the exact number of panels, system size, roof space needed, and estimated cost for your home.

Monthly Electricity Use (kWh) Find on your electric bill. U.S. average: 899 kWh/month.

Peak Sun Hours per Day

Custom Peak Sun Hours

Panel Wattage

Coverage Target (%)

Electricity Rate (¢/kWh)

Your Solar System Estimate

Assumes 80% system efficiency (real-world derate factor). Cost at $3.00/W installed — no federal tax credit applied (expired Dec 31, 2025). Each 400W panel = 21.5 sq ft of roof space.

Peak Sun Hours by U.S. City

Peak sun hours determine how much electricity your panels produce. One peak sun hour = 1 hour of sunlight at 1,000 W/m² intensity. More sun hours = fewer panels needed for the same output.

City	Peak Sun Hrs/Day	Panels for 900 kWh/mo
Phoenix, AZ	6.5	11 panels
Los Angeles, CA	5.5	13 panels
Dallas, TX	5.3	14 panels
Atlanta, GA	4.7	15 panels
Chicago, IL	4.4	16 panels
New York, NY	4.1	17 panels
Boston, MA	3.9	18 panels
Seattle, WA	3.5	20 panels

Panel count for 900 kWh/month, 80% efficiency, 400W panels.

The Formula Explained

The panel count formula every solar installer uses:

Panels = (Monthly kWh × 12) ÷ (Sun Hours × 365 × 0.80) ÷ Panel Watts × 1,000

Breaking it down: Annual kWh need → divided by annual production per kW → gives system kW → divided by panel wattage in kW → gives panel count. The 0.80 accounts for real-world efficiency losses (heat, wiring, inverter, dirt).

How Much Roof Space Do You Need?

A standard 400W panel measures approximately 6.5 ft × 3.3 ft = 21.5 square feet. A 16-panel system requires about 344 square feet of usable roof. For most homes with 1,800–2,500 sq ft of total roof area, roughly 40–60% (720–1,500 sq ft) is usable for solar after accounting for roof orientation, setbacks, and obstructions.

Frequently Asked Questions

How many solar panels do I need for my home?

Most U.S. homes need 15–22 solar panels to cover 100% of electricity use. The exact number depends on your monthly kWh usage, local sun hours, and panel wattage. A home using 900 kWh/month with 4.5 peak sun hours typically needs 16–18 panels at 400W each.

How many solar panels do I need for 1,000 kWh per month?

For 1,000 kWh/month with 4.5 peak sun hours and 400W panels, you need approximately 19–20 panels (7–8 kW system). In a sunnier location like Phoenix (6.5 sun hours), you'd need only 13–14 panels for the same output.

How many solar panels do I need to eliminate my electric bill?

To cover 100% of your electricity bill, size your system to your annual kWh usage. The formula: (monthly kWh × 12) ÷ (peak sun hours × 365 × 0.80) = system kW needed. Divide by panel wattage to get panel count.

How much roof space do solar panels need?

Each 400W solar panel requires about 21 square feet of roof space. A 16-panel system needs approximately 336 square feet of unshaded, south-facing roof area. Most 2,000+ sq ft homes have adequate south-facing roof space.