This Twitter Cover image is 1500×421 pixels. While Twitter recommends 1500×500, I (and other users) have found that leaves an awful lot of the image covered up or cut off, and it seems that this size works much better for many of us. It will fit behind your profile picture as demonstrated above. Note: The area marked as “invisible” is that way for most users. Those with unusual screen dimensions may be able to see some more of the image there.