What is the dimension of a youtube header?

YouTube uses 16:9 aspect ratio players. If you are uploading a non-16:9 file, it will be processed and displayed correctly as well, with pillar boxes or letter boxes provided by the player. If you want to fit the player perfectly, encode at these resolutions:

• 1080p: 1920x1080
• 720p: 1280x720
• 480p: 854x480
• 360p: 640x360
• 240p: 426x240