Facebook, image sizes key dimensions:
Feed posts: wide: 1200 × 630 px (aspect ratio 1.91:1).
square: 1080 × 1080 px also works well. (*Best for Instagram*)
Stories: 1080 × 1920 px (vertical, 9:16 ratio).
Reels: 1080 × 1920 px (same as Stories).
Cover photo (page/profile): 820 × 312 px on desktop, 640 × 360 px on mobile.
Best upload size is 1200 × 628 px to cover both.
Profile picture: 170 × 170 px on desktop, 128 × 128 px on mobile.
Event cover photo: 1920 × 1005 px
Ad images: wide: 1200 × 628 px
square: 1080 × 1080 px
For best results, keep images in JPG or PNG, under 30 MB, and avoid too much text
(Facebook recommends less than 20%). AVOID details near the edges!
WILD CARD info: 4:5 aspect ratio (1080 x 1350 vertical) is the very best for all of Instagram,
especially mobile-first feed. My newest format for FB with auto-feed to Insta, is 1080 x 1350 vertical (4:5 ratio)... BUT I template the important info in an imaginary 1080 x 1080 area, so that it works well for both FB & Insta.
What sizes do you use for posts?