Check Out the Updated EPA National Stormwater Calculator

EPA’s National Stormwater Calculator (SWC) is a desktop application that estimates the annual amount of rainwater and frequency of runoff from a specific site anywhere in the United States (including Puerto Rico). Estimates are based on local soil conditions, land cover, and historic rainfall records.

It is designed to be used by anyone interested in reducing runoff from a property, including

•site developers,

•landscape architects,

•urban planners, and


Watch a short YouTube video about the calculator.

More information and to download the calculator.


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