Your YouTube banner photo will be displayed in different sizes and aspect ratios depending on the end device (i.e. smart TV, computer, tablet, and smartphone). However, you only need to upload one image. It is automatically adapted to the visitor's device when they visit your channel.
The minimum dimension for upload is 2048 x 1152 px. Banner images are displayed largest on smart TVs. If a visitor views your YouTube channel on a smartphone, for example, the banner image is automatically scaled down to fit this screen view. So you should keep in mind that your YouTube banner image will be resized when adapting to different devices, and in the process, parts of the image, especially the edges, will no longer be visible. Therefore, make sure that your banner image’s main information is always visible in all the different display sizes and that there’s no awkward-looking image cropping.