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RAIN GARDEN CALCULATOR

Fill out our Rain Garden Calculator to estimate how much stormwater your rain garden can capture, redirect, filter, and help clean before it reaches local waterways.

Rain Garden Size Calculator (Lake Simcoe Watershed)
Lake Simcoe Watershed

Rain Garden Size Calculator (sq ft)

Use this form to estimate a recommended rain garden area to help slow stormwater and reduce runoff to local waterways. Results are an approximation for planning purposes.

Roof, driveway, or yard area that drains toward the rain garden. You can enter this directly, or estimate it using the downspout section below.
Higher values produce more runoff.

Downspouts on your house (optional)

Use this if you want to estimate roof area draining to the rain garden.
Count all downspouts around the house.
If entered, the calculator can estimate contributing roof area automatically.
This is a simple planning estimate and assumes roof drainage is split fairly evenly.
Default is 1.0" as a simple planning baseline.
Slower soils generally need a larger rain garden.
Rain gardens temporarily hold water before soaking in.
Rain gardens should typically drain within 24–48 hours.

Estimated Results

Note: Final design should consider grading, setbacks from foundations, utilities, and real soil conditions.