A useful guide to social media avatar sizes.
Facebook: Lets you display up to a rectangular image 180 pixels wide x 540 pixels tall while showing avatars of 50×50 pixels elsewhere.
LinkedIn: Sidebar images measure 40 × 40 pixels and profile page images can be 80×80 pixels.
Twitter: Profile pages display images at 73 × 73 pixels while showing avatars at 48 × 48, 31 × 31 and 24 × 24 pixels elsewhere.
Google: Gmail (96 × 96 pixels) and Friend Connect (both 82 × 82 and 40 × 40 pixels) use different images, the image sizes aren’t too different.
Yahoo!: Pulse is Yahoo’s Facebook-like site. The Profile page has your square image at 128 x 128 pixels, but the most-used size is the reduced 32 x 32 that appears near comments.
Myspace: Allows up to 158 × 158 pixels for an image on the profile page, and uses 28 × 28 pixel icons everywhere else.
