The simple math — and the practical details
Panel count is system watts ÷ panel watts, always rounded up. A 7 kW system with 430 W panels needs 17 panels. But the practical part matters more: panels must fit your roof with room for airflow and cleaning access, and strings must match your inverter's voltage windows.
Choosing panel wattage
For US rooftops, 400–450 W panels are the standard residential size: they suit common roof racking and are manageable to carry up a ladder. Larger 545–610 W panels mean fewer mounts and connections, but they are heavier and are used mostly on commercial roofs and ground mounts. If your roof is tight, high-efficiency panels (22%+) deliver more power per square foot.
How many solar panels do I need?
Divide your system size in watts by the panel wattage and round up. A 5 kW system needs 12 of today's common 430 W home panels (11.63 exact); a 10 kW system needs 24. Enter your size above for the exact count, or start from the monthly kWh on your electric bill in the system size calculator if you do not know your kW yet.
How many solar panels can I fit on my roof?
Roughly one panel per 28 ft² once you allow for spacing and walkways — so about 17 panels on 500 ft² of clear roof, or a 7.3 kW array with 430 W panels. Enter your roof area above to see the number for your space. Remember to measure only the shade-free, unobstructed area, not the whole roof.
How many solar panels do I need for a house?
Most homes land between 10 and 30 panels depending on the bill. An average US home using about 900 kWh a month needs roughly 15–25 panels of 430 W, depending on how sunny the location is. The honest way to size it is from the kWh on your own bill, not a rule of thumb.
Do more efficient panels produce more energy?
Per square metre, yes — efficiency matters most when roof space is tight. For the same kW rating, total output is similar; you simply need fewer square feet with high-efficiency panels.
How much roof space does one solar panel take?
A typical 430 W home panel is roughly 21 ft² of glass; with spacing and maintenance walkways, plan 60–70 ft² of roof per kW installed.