The YouTube Channel Banner size (2560×1440px)
YouTube channel art is uploaded at 2560x1440 pixels at 16:9, but it is displayed very differently across devices, which is what makes this banner tricky. The full 2560-wide image only appears on large TVs, while desktop, tablet, and mobile each show a progressively smaller crop from the center of that same file.
Because of this, YouTube defines a central safe area of roughly 1546x423 pixels that is visible on all devices. Your channel name, tagline, upload schedule, and logo must live inside that central band, or they will be invisible to most of your audience who view on phones and laptops.
Everything outside the safe area is bleed that only shows on the biggest screens, so treat it as atmosphere: extended background, color, or texture rather than critical information. A frequent mistake is placing a logo near the corners, where only TV viewers ever see it. Design the meaningful content tightly centered, then let the outer 2560x1440 canvas provide a big-screen flourish.