Quick answer: A typical 440 watt panel takes about 2 square metres, so a 6.6 kW system needs roughly 15 panels and 30 square metres of clear roof. Draw your roof on the free calculator below to get your exact number.
Before any installer visits, you can answer the first big question yourself: how many panels does my roof actually hold, and what system size does that add up to?
The quick maths
A typical residential panel in 2026 is about 1.7 to 1.8 metres long, 1.1 metres wide, and rated around 440 watts, give or take. That works out to roughly 2 square metres per panel once you allow for mounting gaps.
So a common 6.6 kW system is about 15 panels, needing somewhere near 30 square metres of clear, usable roof. A 10 kW system is around 23 panels and needs about 45 square metres.
Why “usable” is the key word
Your roof’s total area and its usable area are two different things. Panels can’t hang over edges, and they have to dodge vents, aerials, skylights and shaded strips. Roofs are also split into faces pointing different directions, and some faces are worth much more than others. A 200 square metre roof might only offer 60 square metres worth putting panels on.
Measure it from a satellite photo
Our free Roof Area & Panel Calculator lets you draw your roof outline on a satellite photo and gives you the usable area, how many panels fit and the system size in kW. No signup, and it works for any address. If you want the full picture, the Roof Azimuth Calculator and Solar Panel Angle Calculator will tell you which way each face points and how much of the ideal yield it captures.
Walking into a quote conversation with those numbers changes the dynamic. You’re checking their work, not taking their word for it.
After the panels go up
Panel count sets what your system can produce on its best day. Whether it keeps producing that is another story; faults and slow degradation eat output quietly, and most owners find out months late. That’s the part PV Fleet handles, with automatic fault detection on any inverter brand.