What is the YouTube channel background proportion size?

the width of a youtube channel, in general, is 960 pixels (however lengths vary for different users depending on what modules are displayed and/or positioned). if you created a 960 pixel wide image, it would be the exact width of the channel elements. but it really it all comes down to each users display or screen resolution. for example, let’s say your display resolution is 1920x1080. someone visiting your channel with the same display resolution would see the entire image. someone with a display resolution of 1024x768 would only see a portion of the middle of the image. it’s not going to be perfect for everyone, but just do what you have to do. sorry if i’m losing you, haha.. this website is really helpful & explains how to figure out your display resolution: http://funadvice.com/r/bhr533fei65