Facebook Event Image Sizes. Facebook event photo size is 1920 x 1080 pixels, a 16:9 ratio. Keep in mind that wider images will most likely have the sides cropped. This is also the same for tall images, the top and bottom facebook event photo will be cropped. Facebook event photo size: The correct size for facebook event photos is 1920 x 1080 pixels.

https://www.skillslab.io/marketing/facebook-cheat-sheet-2018-sizes-and-dimensions/