Criteria

 

Hydrologic Unit Level	Name	Coding Digits	Size (in acres)	Number
1	Region	2
2	Sub-region	4
3	Basin	6
4	Sub-basin	8	250,000-450,000
5	Watershed	10	40,000-250,000	5 to 15
6	Sub-watershed	12	10,000-40,000	5 to 15

 The federal standards for watershed delineation may be found at the following address http://www.ncgc.nrcs.usda.gov/branch/gdb/products/watershed/index.html