Check out the Duplicate Content Tool.
Duplicate content is the term for a filter applied to search engines
queries for which there are two or more relevant pages that are too
similar to each other.
As an effect, pages seen as duplicates of the first relevant results
are filtered out. The aim of that functionality is to provide a
better “results variety.”
This tool visits the two page you ask it analyze: it compares the
two pages in order to look for differences: then it calculates a
percentual estimate of how much difference there is between them.
Give it a try now – it’s free!