SCS Curve Number – Runoff Depth & Abstractions Tool

Quick calculator for SCS CN runoff depth (Q), potential maximum retention (S) and initial abstraction (Ia) for a given design storm. Units: rainfall and runoff in mm; Curve Number 30–100.

1. Inputs CN, Rainfall & AMC

Choose how you want to specify Curve Number (single CN or composite from land‑uses), then enter design rainfall and antecedent moisture condition. The tool follows the standard SCS runoff equation.
Composite mode lets you enter up to four land‑use / soil‑group areas with their own CN values.
Event runoff depth Initial abstraction Runoff ratio
Total event rainfall depth over the catchment (point or areal‑average). Use your IDF / hyetograph tools for this.
CN is interpreted as AMC II and internally adjusted for AMC I / III using standard NRCS relations.
Only used in exported XLSX / PDF.