Panel count and roof area
Check how many panels fit and whether the roof is large enough.
Updated 2026-07-17 · Formula version appears with every result.
Preparing the calculator…
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Data confidence
Moderate
Evidence used
Uses target system size, panel dimensions, roof dimensions, slope, setbacks, and obstruction allowance.
What can vary
Structural capacity, exact roof geometry, access paths, fire rules, and shading need a site inspection.
Planning use
Educational estimate only. Confirm the final design and quotation with qualified professionals.
How this estimate works
Calculations are versioned, reviewed, and reproducible. Inputs are validated and planning ranges are used instead of false precision.
Results support early decisions. Confirm utility rates, equipment specifications, site conditions, and professional requirements before committing money. Review the methodology and source policy before treating any estimate as decision-ready.
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Before using the calculator
What this calculator estimates
Estimate panel count, array footprint, and preliminary roof fit from target kW, panel wattage, dimensions, roof size, and obstructions.
Who it is for
Property owners checking whether a target system is physically plausible before a measured roof layout and structural review.
Inputs and methodology
Panel count is target kW divided by panel kW and rounded up. Array footprint multiplies panel count by panel dimensions, while usable roof area reduces the entered roof rectangle by the obstruction allowance.
Required inputs
- Target system capacity and panel wattage
- Panel length and width
- Roof length, width, and obstruction allowance
Philippine planning assumptions
- The roof is simplified as one usable rectangle.
- Walkways, edge setbacks, hips, valleys, orientation, row spacing, drainage, fire access, structural limits, and mounting details require a real layout.
Worked example
A 5 kW target using 550-watt panels requires 10 panels after rounding up. Panels measuring 2.28 by 1.13 metres occupy about 25.8 square metres before spacing and access allowances.
How to interpret the result
A “fits” result means only that the simplified area is sufficient. It does not confirm structural capacity, shade performance, code clearances, waterproofing, orientation, or installation access.
Use the result as a comparison baseline: change one assumption at a time, keep the original inputs, and ask installers to explain why their written estimate differs.
Common mistakes
- Using gross roof area without setbacks and obstructions
- Assuming every roof plane has the same shade and orientation
Related questions
Does enough area mean the roof is suitable?
No. Roof condition, structure, waterproofing, wind exposure, shade, orientation, electrical routing, access, and local requirements still need assessment.
Why can the final panel count be lower?
Required walkways, edge clearances, roof hips and valleys, access, shading, structural zones, drainage, and mounting geometry can reduce usable roof area.
Limitations and disclaimer
- The result is an educational planning estimate, not a quotation, site survey, electrical design, or engineering approval.
- Verify current rates, equipment, roof conditions, utility rules, and written installer assumptions before spending.
Last reviewed 2026-07-20