Use this free interactive solar panel calculator to find out how many solar panels fit on your roof. Formula: Panels = (Roof Area × Usable % × (1 − Spacing Loss %)) ÷ Panel Area → Total Capacity (kW) = Panels × Panel Wattage ÷ 1000. Determining how many solar panels fit on. The rule of thumb for 2026: about 1 kW of solar per 70 square feet of total roof area, or roughly 28 sq ft of total roof per modern 400W panel after fire-code setbacks. It calculates the maximum number of panels that fit on the available roof surface, taking into account important factors such as orientation, inclination. The Solar Power Roof Area Calculator is a valuable tool designed to help users estimate the required roof area for installing solar panels. Draw your roof outline on the satellite map, choose your panel size, and the tool instantly fills in a grid of panels — then calculates estimated capacity, annual energy output, and CO2 savings. → You can install approximately 10–12 kW 2,000 sq.
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