What is an SCS Calculator? Formulas and Free Online Tools An SCS Calculator is a digital tool used by engineers, hydrologists, and builders to estimate stormwater runoff. It stands for Soil Conservation Service (now called the Natural Resources Conservation Service or NRCS).
When heavy rain hits the ground, some water sinks into the soil, and some water flows over the land. This flowing water is called surface runoff. Knowing how much water will run off helps experts design safe drainage pipes, rain gardens, and flood protection systems. How the SCS Method Works
The calculator uses a special value called a Curve Number (CN). The Curve Number ranges from 1 to 100.
A low curve number (like 50) means the ground absorbs water easily, like a dry forest.
A high curve number (like 98) means water cannot sink in, like a paved parking lot.
To find the right Curve Number, the tool looks at two main factors:
Soil Type: Soils are split into four groups (A, B, C, and D) based on how fast they absorb water. Group A absorbs water quickly, while Group D is heavy clay that blocks water.
Land Use: This is what covers the ground, such as trees, grass, gravel, or asphalt.
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