How this calculator works
Measured slope area needs no pitch correction. Footprint mode multiplies horizontal area by sqrt(1 + pitch²). Divide area including waste by the installed panel coverage and round up. The installed dimensions must already remove side and end laps. An area quotient does not optimise panel courses or custom full-length sheets; make a panel layout before ordering. Cost includes the entered panel price and area-based installation rate only.
Formula
roof area = horizontal area x sqrt(1 + (rise/run)²); panels = ceil(area x (1 + waste)/(installed panel length x installed panel width)); cost = panels x panel price + net area x installation rate.
Worked example
A 10 m by 8 m footprint at 9:12 pitch has a 1.25 multiplier and 100 m2 roof area. With 10% waste and panels covering 2 m2 each, buy 55 panels.
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Frequently asked questions
Should panel width include the side lap?
Use installed cover width, which is smaller than overall sheet width. Apply the same principle to end laps.
Does this include flashings and screws?
Only if you include them in the entered area-based extras. Ridge, valleys, perimeter trims and fasteners need their own takeoff.
Can I use it for several roof pitches?
Calculate each pitch or roof section separately and sum the results. One multiplier assumes a common slope across the entered footprint.