Solar Panel Layout Calculator
Enter your usable roof area, panel wattage and local peak sun hours to find out how many panels fit, your total array size in kWp, and estimated annual energy output. A visual panel grid shows the layout at a glance.
Last updated: May 2026
Area after setbacks, ridgeline, and obstructions — not total roof area.
Standard residential panel: ~2.0 m² (1.0 m × 2.0 m). Check your panel datasheet.
Enter usable roof area and panel details above.
80% system efficiency applied. Panel count uses floor (can't exceed available area).
How to use this calculator
Enter the usable roof area first — not the total roof size. Deduct ridge lines, valleys, roof windows, chimneys, and the mandatory setbacks from edges and obstacles (typically 0.5 to 1.0 m from each edge depending on local fire codes). A 60 m² roof section often yields 40 to 45 m² of usable area after setbacks.
The panel area field defaults to 2.0 m², which matches the dimensions of a standard residential 400 Wp monocrystalline panel (~1.0 m wide × 2.0 m tall). Larger 550 W panels are roughly 2.4 m². Check your chosen panel's datasheet for exact dimensions.
Reference: common panel sizes and fits
| Roof area (m²) | Panel size (m²) | Panels that fit | Array at 400 W |
|---|---|---|---|
| 20 | 2.0 | 10 | 4.0 kWp |
| 30 | 2.0 | 15 | 6.0 kWp |
| 40 | 2.0 | 20 | 8.0 kWp |
| 30 | 2.4 | 12 | 4.8 kWp (at 400 W) |
| 40 | 1.7 | 23 | 9.2 kWp (at 400 W) |
| 50 | 2.0 | 25 | 10.0 kWp |
Frequently Asked Questions
How much roof area does a typical home solar installation need?
A 6 kWp system using 400 W panels (15 panels at 2.0 m² each) needs 30 m² of usable area. A 10 kWp system (25 panels) needs 50 m². In practice most European detached homes have 30 to 60 m² of south- or southwest-facing usable roof area, enough for 6 to 12 kWp. Setbacks, chimneys, skylights and ridge lines typically reduce available area by 20 to 40% compared to total roof section area.
Why use "usable" area rather than total roof area?
Building codes in most countries require setbacks of 0.5 to 1.0 m from roof edges, ridgelines and obstructions for fire access and structural load reasons. A panel that overhangs an edge is not installable. Subtract those margins before entering the area here. Using total roof area will give you a panel count that cannot be installed in practice and will overstate your system capacity.
What is the standard size of a residential solar panel?
Modern 60-cell monocrystalline panels (300 to 380 W) measure roughly 1.65 m × 1.0 m (1.65 m²). The newer 72-cell and 400 to 450 W panels are typically 2.0 m × 1.0 m (2.0 m²). Large format 550 to 600 W panels used in commercial installations are around 2.4 m × 1.1 m (2.6 m²). Always check the datasheet for the specific panel you are evaluating.
How does this calculator differ from the Solar Panel Output Calculator?
The Solar Panel Output Calculator starts with a known panel count and calculates energy output. This calculator starts from a roof constraint: it tells you the maximum panels that physically fit in your available area, then estimates the resulting output. Use this one first to find your maximum array size, then use the output calculator to model production scenarios in detail.
Can I fit more panels by using smaller panels?
Yes, but the gain is limited. Switching from 400 W (2.0 m²) to 300 W (1.65 m²) panels on a 30 m² roof adds 3 extra panels (from 15 to 18) but reduces panel wattage, giving 5.4 kWp instead of 6.0 kWp — less total power despite more panels. Smaller panels make sense when roof access paths or thin strips of area exist that a large panel cannot cover. For maximising energy from a constrained area, higher-wattage large panels are usually better; for filling awkward shapes, smaller panels offer more layout flexibility.