The YouTube Shorts Cover size (1080×1920px)
YouTube Shorts play in a vertical, full-screen player, so the cover you pick is a 1080x1920 pixel image in a 9:16 ratio. This is the still that represents your Short on your channel's Shorts shelf and in search results, and building it at the native size means it fills the tall player cleanly and stays sharp when YouTube generates the smaller thumbnails used across the app.
The important difference from a regular YouTube thumbnail is orientation and safe area. Shorts covers are vertical, and when they appear as thumbnails on the channel page they are cropped toward a narrower vertical or square-ish rectangle. On top of that, the live player overlays the title, channel name, like and comment buttons, and the progress bar. Keeping your headline and subject in the central vertical band, away from the bottom third and the right edge, ensures nothing important disappears behind the interface.
Because Shorts are surfaced heavily through recommendation feeds, a bold, legible cover with a short hook does more work than a detailed scene that turns to mush at thumbnail scale. Resizing your artwork to exactly 1080x1920 first keeps text crisp and avoids any last-minute stretching by the upload flow. This tool resizes 100% in your browser with no upload, it is free, and it locks the 9:16 aspect ratio. YouTube updates its Shorts overlays and thumbnail crops regularly, so verify the current safe zones before publishing.