In the past, logos came in all different sizes and shapes—whatever symbol best matched the type of service the organization provided. Today, graphic designers have to alter their design to accommodate social media applications. You need to have a square version of your logo to use in social media, such as Facebook, blogs, and other square applications.
The Facebook profile image that Facebook provides for people and businesses is square. You need to provide an image at least 180 pixels x 180 pixels. (72 pixels equals 1 inch.) https://www.facebook.com
Gravatar stands for Globally Recognized Avatar, an image that appears beside your name when you post a blog or comment on a blog. Avatars identify your posts on blogs or websites, especially WordPress. The Gravatar Profile Image should be at least 310 pixels x 310 pixels. If you upload an image that is not square, it will get cropped. https://en.gravatar.com
A Favicon is a logo or icon on a website address bar. The maximum size is 150 kb. It should be square. This website will generate the HTML required for a favicon that you can place in the HTML of your website, so it shows up on your address bar: http://www.faviconr.com