Here’s a great diagram showing all of the specific measurements and dimensions for your Facebook header.

Profile Image:
Uploads at 180px by 180px
Displays at 160px by 160px
Position from the left of the cover image is 23px
Position from the top of the cover image is 210px

Cover Image:
Uploads and displays at 851px by 315px

Also have Google Plus? Check out Google Plus Dimensions!