Facebook event cover size
Mobile crops shorter and overlays the event details.
Cropped in your browser · your image is never uploaded
1920 × 1005, which is roughly 1.91:1. Mobile crops it shorter and overlays the event name and date across the bottom, so keep that area clear.
How to use the facebook event cover size
Event covers get treated like a poster and that is usually a mistake, because Facebook already prints the event name, date and location underneath and, on mobile, partly over the image. Repeating all of that in the artwork produces a cluttered result where the two sets of text fight each other. The cover works better as a single strong image with at most a short line of type. The other consideration is that the cover is what appears in a shared link and in the feed when someone marks themselves as going, so it does most of its work at small size in a busy feed rather than on the event page itself.
Questions
1920 × 1005, about 1.91:1.
Facebook overlays the event name and date on mobile. Keep the lower area of the image clear.
Generally no — Facebook already shows it, and repeating it clutters the image.
On the event page, in the feed when someone responds, and in shared links.
Yes, Facebook accepts a video cover for events, at the same aspect ratio.