Watershed hydrologic units (HU) are generally subdivided into 5 to 15 units. The average size of an 8-digit sub-basin hydrologic unit is about 450,000 acres. The typical 10-digit watershed size is 40,000 to 250,000 acres, while the typical 12-digit subwatershed is 10,000 to 40,000 acres. 8- and 10-digit watersheds can be derived from 12-digit watershed shapefiles.