EPA National Stormwater Calculator

Free EPA tool for estimating stormwater runoff at a site and testing green infrastructure scenarios.

The National Stormwater Calculator is a site-scale stormwater estimation tool that supports runoff analysis and green infrastructure planning decisions. It pulls soil, topography, and rainfall data for a given location and lets users model how different low impact development controls change runoff volume and frequency. It is a practical starting point for municipalities and watershed groups scoping green stormwater infrastructure before commissioning engineering work.