What are the factors that affect the size of index partitions in Sharepoint 2010? Is size of documents a factor? Any explanation would be appreciated.
The Technet article Estimate performance and capacity requirements for SharePoint Server 2010 Search provides the following formula to estimate the size of index partitions:
The size of the index ultimately depends on the size and the contents of the documents that are indexed. Text heavy documents will yield a larger index while image heavy documents will yield a smaller index. But I think you are on the safe side when using a factor of 0.35 as suggested by Microsoft.