I ran across this handy infographic that details the current Facebook photo size dimensions.
The two most important dimensions are the profile picture and you cover photo. These are highly visible parts of your Facebook persona. I highly recommend that you crop your photo and upload the EXACT SIZE* recommended, otherwise Facebook will shrink it for you and you may not like what you see.
*With your profile picture you need to upload the 180×180 size…for some reason the actual size of 160×160 doesn’t meet Facebook’s minimum size requirements.