Facebook link thumbnail images are now bigger than ever. However, it’s important that you understand what all specifications are to optimize your posts for advertising.
The image above covers the specs for Desktop News Feed only. Here’s a quick reference that’ll help you figure out all Facebook ad sizes, including ideal dimensions for Desktop News Feed, Mobile and Sidebar for nine different ad types.
[NOTE: This data is pulled from Facebook's Ads and Sponsored Stories Guide.]
A Few Thoughts
Why does Facebook recommend a 1200 pixel width for all images? One would assume the largest image for each unit’s placement would be sufficient. But the larger size is likely for optimizing the full screen image view (think photo and video viewer).
It’s also odd that Facebook features square images and videos for all placements, but then they recommend a 4:3 aspect ratio for photos and 16:9 for videos. The 16:9 makes sense for videos (it’s standard for viewing), but the photos recommendations is a bit odd.