Roof Drain Calculator
Estimate the number of roof drains required based on roof area, rainfall, roof slope, and drain pipe size.
Total Roof Drains Required
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Rounded up to the next whole drain
Roof drain sizing: This calculator estimates the number of roof drains required using roof area, peak hourly rainfall, roof slope, and selected drain pipe capacity.
Number of Drains =
Roof Area × Rainfall Factor
÷
(Pipe Capacity × Slope Factor)
Roof area entered in ft² is automatically converted to m² before calculation. This tool provides an estimate; final drainage design should consider local rainfall data, hydraulic layout, and applicable building or plumbing requirements.