Roof panel layout
How Many Solar Panels Fit on My Roof?
Measure the usable roof area after your own setbacks, vents, and access paths. Compare portrait and landscape rows and columns to estimate panel count and nameplate kW. This is a simple rectangular fit, not a final layout or structural approval.
Measure the usable roof rectangle
Your planning estimate
Local calculationEnter your values, then calculate. Results will show the formula inputs and rounding used.
Formula used
panels per dimension = floor[(usable dimension + gap) ÷ (panel dimension + gap)]The gap is counted only between neighboring panels. Both orientations are calculated with whole rows and columns; the result selects the higher panel count and recomputes installed nameplate power from that count.
See the full assumptions and rounding policy.
Maintenance and verification
The calculator calls the shared, tested TypeScript calculation modules documented in the methodology. Automated tests cover published examples, invalid inputs, rounding, and result invariants.
SolarMathKit maintains this implementation. The review is an internal technical check, not an independent engineering certification.
Worked example: a 6m × 4m usable rectangle
The panels are 2m × 1.1m, the entered gap is 0.05m, and each panel is rated 440W.
- Portrait fit: 2 rows × 3 columns = 6 panels.
- Landscape fit: 5 rows × 1 column = 5 panels.
- The portrait layout fits one more whole panel.
- 6 panels × 440W = 2,640W installed nameplate power.
Common mistakes to avoid
- Entering total roof dimensions instead of the clear usable rectangle.
- Ignoring vents, hips, valleys, access paths, mounting zones, and project setbacks.
- Using panel dimensions from a different product variant.
- Treating a geometric fit as structural or installation approval.
Questions people ask
Does this calculate roof setbacks?
No. Setbacks and access rules vary by project and jurisdiction. Enter dimensions after applying the constraints that govern your installation.
Does it model several roof faces?
Not in one calculation. Run each clear rectangular roof face separately and keep orientation, shade, and electrical design decisions distinct.
Why compare portrait and landscape?
Rotating a rectangular panel changes how many whole rows and columns fit. The higher count is not automatically the best electrical or mounting design.
Is the panel count a final layout?
No. It is a planning estimate for a simple rectangle. A final layout must check measurements, structure, mounting hardware, shade, equipment rules, and applicable requirements.