Sprout Social has a great guide to social media image sizes
Coming back to school after a nice summer and dusting off your staff’s social accounts only to find they need quite a bit of TLC? Did your social network make some design changes that have your profile looking a bit wonky? Never fear, Sprout Social is here to help. The have an online guide that is updated with the latest specs, not only for image sizes relating to your profile, but optimal image sizes within feeds as well. They offer guidance in the following networks:
Head on over and give it a look here. They also have a Google Doc you can access that has the dimensions in a tabbed spreadsheet form. They even tell you how to turn on notifications so you can be alerted when sizes change. Make sure to pass these great resources along to whichever staffers manage your accounts so they can use it this year to help make your social presence as strong and professional looking as possible.