You can calculate this pretty easily if you have sufficient reputation to view the vote breakdown.
If you have more than 1000 rep on the specific Stack Exchange site, you can view how many upvotes or downvotes were cast by clicking on the number next to the post. A downvote costs the owner of the post 2 reputation, while an upvote gives a person 10 reputation. So for example this post earned me
(2 x -2) + (2 x 10) = 16 rep:
If you have < 1000 rep, you could use the "View Vote totals" without 1000 rep userscript / Chrome extension.