I came across a video about treatment area calculation on USGBC website: https://www.usgbc.org/resources/reducing-rainwater-runoff-volume-case-example-and-calculation-walk-through-part-2-1
For the case study discussed in the video, it referred to MDE's simple equation for estimating surface area, an equation based on the 2000 Maryland Stormwater Design Manual (starting at 1:30 of the video). I noticed the surface area constant of C does not come with any unit, and this is what confuses me: unless the constant has its unit in inch, the result solved from this equation will be a volume instead of an area.
So, does the surface area constant C has its unit in inch? If yes, can this simple equation also be used to estimate surface area that is measured in SI unit such as square meter?