This is how we calculate all click and open rates 

Formulas 
Click rate = Unique clicks divided by the number of successfully delivered emails
100 delivered emails with 10 unique clicks = 10% click rate 

Open rate = Unique opens divided by total emails successfully delivered
1000 emails delivered with 100 unique opens = 10% open rate 
*We only track open/click rate for unique opens/clicks, not total opens/clicks.  
*Unique means it was only done once.  

Example: If the recipient Bob opens the email twice, and clicks the same one link 5 times we'll only report 1 unique open and 1 unique click. 
If Bob clicks 3 different links in the same email that would be counted as 3 unique clicks.