A Cantilever is one-half of a span. Therefore to report deflection in a consistent ratio, for example L/480, the length of the cantilever is mulitplied by 2. If the cantilever controls in deflection the resulting control value is reported as 2xL/480.
This is in accordance with the IRC 2009, Table R301.7 Note(b):
For cantilever members L shall be taken as twice the length of the cantilever.