The Essential Cheat Sheet for Social Media Cover Photo Dimensions [+ Pre-Sized Templates] - HubSpot
The Ultimate Social Media Design Blueprint 2015 infographic
Social Media Cover Photos Infographic
Want fantastic hints on social media?
The Mega Guide to Ideal Image Sizes for Your Social Media Posts: Guidelines for All 6 Major Social Networks
Social Media Cover Photo Dimensions that Work - 2015 edition
How to Size Images on Social Media: A Cheat Sheet (Infographic)
Image sizes for LinkedIn, optimized and up-to-date, courtesy of Mashable Australia.