Enter your roof face dimensions to see how many panels fit. Standard 400W panels are 66 × 40 inches. NEC requires a 3 ft setback from all roof edges.
Roof Dimensions
ft
Longer dimension of the roof face.
ft
Shorter dimension (ridge to eave).
Pitch multiplies the actual roof surface area.
Panel Configuration
W
Portrait is most common on residential roofs. Landscape may fit more panels on wide, shallow roofs.
⚙ Advanced Options▼
in
Long dimension. Default: 66 in.
in
Short dimension. Default: 40 in.
ft
NEC 690 requires 3 ft from all edges.
%
Deducts vents, hips, skylights.
0.5 in
0 in (flush)3 in6 in
Gap between adjacent panels in racking. Typical: 0.25–0.5 in.
Panels That Fit
—
Solar Panels
Enter dimensions to calculate
System Capacity
—
kWp DC
Usable Roof Area
—
sq ft
Panel Coverage
—
of usable area
Actual Roof Area
—
sq ft
Layout— cols × — rows
Pitch Factor—
Usable Length × Width—
Panel Footprint—
Roof Layout Preview
Top-down view
Want to calculate annual energy yield? Use our Solar Panel Sizer to enter your system capacity (X kWp) with your location for location-specific yield, peak sun hours, and savings estimates.
Methodology:
Actual Roof Area = Length × Width × Pitch Factor, where Pitch Factor = √(1 + (rise/run)²). For a 4:12 pitch: √(1 + (4/12)²) = 1.054.
Usable Length = (Length − 2 × Setback), Usable Width = (Width − 2 × Setback).
Usable Area = Usable Length × Usable Width × Pitch Factor × Usable Area %.
Panel columns = ⌊Usable Length ÷ Panel Footprint Width⌋.
Panel rows = ⌊Usable Width ÷ Panel Footprint Height⌋.
Total Panels = Columns × Rows.
System kWp = Total Panels × Panel Wattage ÷ 1,000.
Panel dimensions are measured as flat projections (horizontal footprint) on the roof surface — pitch factor is applied to the roof area, not individual panel sizing.
This tool gives a planning estimate. Actual layout depends on racking system, roof penetrations, fire code pathways, and AHJ requirements. Always confirm with a licensed solar designer.
SurgePV Platform
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