For the majority of posts and ads on Facebook and Instagram, we suggest using square (1:1 aspect ratio) photos with a recommended image size of 1080 by 1080 pixels. The square image recommendation is thanks to a big change made recently by Facebook when it began moving away from the previously recommended landscape (1.9:1 aspect ratio) format.
For stories, which can be used as ads and organically, the recommended image should be fullscreen vertical (9:16 aspect ratio). When it comes to story design, Facebook suggests: "Consider leaving roughly 14% (250 pixels) of the top and bottom of the image free from text and logos to avoid covering these key elements with the profile icon or call-to-action. This means, if your image is 1080x1920, ensure key elements appear within a 1080x1420 title-safe area."
Pro Tip
To make life easier for your designers, you can create social media images in portrait format (9:16) for Stories and then crop it to square format (1:1) for other Posts. Another added advantage of using square images for all Facebook posts (as opposed to the previously accepted landscape (1.9:1) format, is that it makes crossposting from a Facebook post to an Instagram post extremely easy when using Creator Studio.