I have been unable to find the exact value of one point of blocking. The unofficial Elder Scrolls pages and other wikis do not list a value for blocking.
As an example, for heavy armor one point adds 0.4% armor.
The block value seems important because I want to find out how much fortify block to enchant on my stuff. the USEP lists the max block mitigation as 85% (if you are looking at this page) or 80% (if you are looking at this page).