What units are 'reads' and 'writes' in dm_exec_query_stats
Reads and writes are expressed in terms of "the number 8K pages." It should be documented better on the page you reference, but you can piece this together from other areas of the documentation, e.g. from Reading Pages:


  A logical read occurs every time the Database Engine requests a page from the buffer cache. If the page is not currently in the buffer cache, a physical read first copies the page from disk into the cache. 


And from Understanding Pages and Extents:


  In SQL Server, the page size is 8 KB.