I had to create a number of Facebook and Twitter accounts for one of the companies where I am employed. As I had to put Avatars to each and every new account. I therefore had to resize the company logos to fit the to the avatar dimensions..
It took me a bit of research until I found the proper picture dimensions. Here are the dimensions:
For facebook page Avatar the good picture width / height dimensions is a square like:
If however you prefer to have a sky scraper picture in Facebook, this is possible as thumbnail pictures up to 180×540 w/h pixels are showing up in FB.
At most cases FaceBook automatically resizes the uploaded picture and generates a thumbnail which in most pictures looks okay, however in some odd picture dimensions the picture preview might be messy, so its better to ship the profile pic in standard square size like 151×151, 256×256, 313×313 etc.
For Twitter page Avatar the fixed picture width / height dimensions is:
In Twitter again the avatar picture should be a square like, to have twitter during upload automatically resize and make a good looking pic thumbnail. If some picture with a non square dimensions is uploaded as an Avatar for twitter account usually, twitter's pic auto resize server side program chops parts of the picture. This is not a bug but expected behaviour. In Twitter another requirement is that the uploaded avatar image does not exceed 700kb, trying to puload a picture over 700k fails.
In both Facebook and Twitter the uploaded Avatar logo should be in format JPEG, GIF or PNG .
To resize the company logo pictures for FB and Twitter, I used GIMP 's:
Image -> Scale Image
I've red some people claiming the size of the Avatar logo in Facebook could have some impact in terms of e-marketing, but I'm not sure if this is a fact or some false rumour. Anyways it is sure that a wide sky scraper like picture allows you to show more even from the profile and maybe through the picture have larger influence over the audience.