The Curve Number Calculator allows the curve number to be calculated for the SCS runoff method.

As different options are selected from the drop-down list, the appropriate curve number is selected. Clicking OK will select the currently displayed curve number.

Curve Numbers are calculated by looking up the values in the tables 2-2a to 2-2d in document  TR-55.pdf, authored by Natural Resources Conservation Service (NRCS). TR-55 is a widely used approach to hydrology in the US.