Facebook – maximum picture size
November 19th, 2009
If you are uploading pictures to Facebook, the largest dimension (either width or height) is 604 pixels. If you upload a picture with a width or height larger than that, Facebook will resize it, maintaining the aspect ratio, but who knows what algorithm they are using to do that.
If you want the best quality photo, load your photo into Photoshop, make the largest dimension 604 pixels, save it, and then upload it to Facebook.