Solar Panel Square Footage Calculator
Calculate available roof square footage for solar panels. Standard residential panels are about 17.5 sq ft each (65 × 39 inches) and produce 350-400 watts.
Solar Roof Area Calculator
How much roof space per panel
Standard residential solar panels are 65 × 39 inches = 17.6 sq ft per panel. Including the framing and rail spacing between panels, plan on ~20 sq ft per installed panel.
100 sq ft of usable roof space holds about 5 panels = ~1,750 watts (1.75 kW). 500 sq ft holds about 25 panels = ~9 kW. A typical 6 kW residential system needs around 350 sq ft of clear south-facing roof.
Roof area limitations
Code typically requires a 3-foot setback from the ridge and from gable ends for fire access. Some jurisdictions require setbacks from valleys and dormers as well. These setbacks can reduce usable area by 30-50% on small or complex roofs.
Shading from chimneys, vents, and adjacent buildings further reduces effective area. South-facing roof planes are most productive; east and west still produce well; north-facing roofs in the northern hemisphere are usually not viable.
Pro tips
Use roof slope, not floor area
A pitched roof has more surface area than its floor footprint. A 7/12 pitch roof has about 1.16× the area of the floor below it.
Account for setbacks early
Don't calculate "roof area × panel count" - first subtract code-required setbacks. The usable area is often 60-70% of the gross roof plane.
Solar production varies by orientation
A south-facing 6 kW system in Phoenix produces about 9,500 kWh/year. The same system facing east drops to ~7,500 kWh. Use a tool like PVWatts for precise estimates.
Get a site assessment
Solar installers offer free assessments that include shading analysis, roof condition, and electrical panel capacity. The square footage calc is a starting point only.