Free Solar Panel Area calculator with clear step-by-step results.
Panel count comes from target capacity divided by panel rating, rounded up because you cannot fit a partial module. Multiplying by panel area gives the glass area, and the spacing factor adds the row gaps, edge setbacks and access walkways that any real installation needs.
Panel count
Panels = ceil(target kWp x 1000 / panel watts)
Roof area
Area = panels x panel length x panel width x row spacing factor
Roof-mounted solar affects structural loading, weathertightness and fire access, and is subject to permitting and grid connection approval. Have the design assessed by a qualified installer.
Around 1.05-1.15 for a flush-mounted pitched roof, and 1.5-2.5 for a flat roof with tilted rows where inter-row shading must be avoided.
Many jurisdictions require clear pathways along ridges and edges for firefighter access, which can reduce usable roof area substantially. Check local requirements before committing to a layout.