According to Twitter Help Center: they suggest the following dimensions:
– Profile pic: 400 x 400 px
– Cover photo: 1500 x 500 px
The size of the preview pic has also been changed. Now, it’s just big enough so that you don’t have to exit the stream to see it.
But, above all, this change was essentially oriented to allow brands to optimize communication campaigns easier through storytelling, the new trend in content marketing that uses videos and/or pictures to tell a story that aims to bring brands closer to their audience avoiding the old-fashioned TV ad.
The dimensions of Twitter’s picture for the in-stream, must be of 440 x 220 px, vertically centered with a radius of 2:1 and it can’t be more than 3MB. If you want the preview pic you see on of the stream to be the same as the original, it can’t exceed the following measurements: 1024 x 512 (aspect 2:1).
The new cover’s aspect (radius) remains the same 16:9, but what’s shown is way smaller. You probably have noticed, as users, you didn’t need to change anything manually, however, there are details that can be optimized and here are the specific dimensions you should use to achieve them:
– The maximum size of the cover image can be of 2120 x 1192 px
– The minimum size of the cover image must be more than 480 x 270 pix
– The size of the profile picture is still of 250 x 250 pix
How it looks on devices:
G+’s design is responsive, so pictures automatically adapt to different devices. However, if you want to ensure maximum quality on all screens, tablets, or smartphones, we recommend you upload them with a size of at least 920 x 250 pix but not more than 1080 x 608 pix, otherwise some of the information will get lost.
If you want to optimize a picture for your brand or for your professional profile we recommend you use the 1080 x 608px resolution, which keeps the most important information in the center.
Facebook has largely kept their image sizes about the same over the last few years. But it is essential to size your images properly before you upload to facebook or you will find that the images either get cropped or are too small and will not be accepted when you attempt to update your profile or cover photos. This is especially important for Facebook business pages!
As always please feel free to comment and ask questions!