As a simple guideline, copying a table and its indexes requires space equal to the current space used by the table and its indexes, plus about 20% additional room. However:
If data modifications have created many partially-full pages, space required for the copy of the table can be smaller than the current size.
If space-management properties for the table have changed, or if space required by fillfactor or reservepagegap has been filled by data modifications, the size required for the copy of the table can be larger.
Adding columns or modifying columns to larger datatypes requires more space for the copy.
Log space is also required.