The Ridiculously Exhausitive Social Media Design Blueprint features all of the major design dimensions for all of the major platforms, including Facebook, Twitter, Google+, LinkedIN, YouTube, Pinterest and the most recent entry, Instagram.
Here's the one for your Instagram profile:
From A Guide To Social Media Images (Infographic) @ originalginger.com:
Since there are so many social media options available now we find it helpful to have a guide to refer to when we are preparing design elements and images.
Here's the one for YouTube:
By the way: if you often upload videos to your YouTube channel, make sure to subscribe to http://youtubecreator.blogspot.be/ - the official YouTube Partners & Creators blog.