Taken from https://www.falcon.io/insights-hub/topics/social-media-management/social-media-images-guides/
Facebook profile picture size: 180 x 180
Facebook cover photo size: 851 x 315
Facebook link image size: 1200 x 628
Facebook image post size: 1200 x 900
Facebook highlighted image size: 1200 x 717
Facebook event image size: 1920 x 1080
Facebook video size: 1280 x 720
Maximum Facebook video length: 240 minutes
Facebook ad size: 1280 x 628
Facebook video ad size: 1280 x 720
Facebook Story ad size: 1080 x 1920
LinkedIn company logo size: 300 x 300
LinkedIn cover photo size: 1536 x 768
LinkedIn Dynamic Ads size: 100 x 100 (company logo)
LinkedIn Sponsored Content image size: 1200 x 628
Personal pages:
LinkedIn profile picture size: 400 x 400
LinkedIn background photo size: 1584 x 396
LinkedIn post image size: 1200 x 1200 (desktop) 1200 x 628 (mobile)
LinkedIn link post size: 1200 x 628
LinkedIn video size: 256 x 144 (minimum) to 4096 x 2304 (maximum)
Maximum LinkedIn video length: 10 minutes
Twitter profile picture size: 150 x 150
Twitter header size: 1500 x 500
Twitter post image size: 1024 x 512
Twitter card image size: 1200 x 628
Twitter video size: 720 x 720 (square), 1280 x 720 (landscape), 720 x 1280 (portrait)
Maximum Twitter video length: 140 seconds
Twitter ad size (image): 1200 x 675
Twitter ad size (video): 720 x 720 (square), 1280 x 720 (landscape), 720 x 1280 (portrait)
Instagram profile picture size: 180 x 180
Instagram photo sizes: 1080 x 1080 (square), 1080 x 566 (landscape), 1080 x 1350 (portrait)
Instagram Stories size: 1080 x 1920
Minimum Instagram video sizes: 600 x 600 (square), 600 x 315 (landscape), 600 x 750 (portrait)
Maximum Instagram video length: 60 seconds
Minimum Instagram image ad size: 500 pixels wide