SCS Curve Number – Runoff Depth & Volume Tool

Quick‑check calculator for direct runoff depth and volume using the NRCS SCS Curve Number method (TR‑55).
Handles CN adjustment for antecedent moisture conditions I / II / III, with outputs in depths and volumes.

1. Inputs & Settings Rainfall, CN & Area

Enter storm rainfall depth, Curve Number (for AMC II), antecedent condition, and drainage area. Tool returns runoff depth, loss depth, and runoff volume.
Total event depth at the catchment (from IDF / design storm), not intensity.
P and runoff depths are reported in both mm and inches.
Composite CN for average antecedent condition (II). Typical range 30–98.
CN is automatically adjusted from CNII using standard TR‑55 formulas.
Total tributary area contributing to the outlet.
Internally converted to m²; runoff volume is returned in m³, ha·m and acre‑ft.
For documentation only; CN method here uses total depth P, not duration.
Used to label the event (e.g. 25‑year storm); no effect on calculations.