When I first started on Pinterest I would often pin images only to have them look like crud after they were uploaded. I did some playing around in the lab and came up with a good cheat sheet for pinning perfectly sized images that will look great on Pinterest.
Cheat Sheet for Pinterest Image Sizes
The profile image will be viewed at 165×165. Pinterest recommends that you upload an image that is 600×600 and it will scale it down for you.
The pin image in the feed will be 238 pixels wide and will adjust the height based on the image.
Once you click on a pin from your feed the pin can expand all the way up to 735 x adjusted height. This is where you want to be sure that you have a great high-resolution photo.
The complete board image is 238 x 284. Keep in mind that some of the board will be covered by preview images of pins within the board.
Part of the board image is going to be covered by the previews to other pins on that board. Make sure that your board image stays inside these parameters (214 x 147) in order for it to look great.
Keeping these image sizes in mind will help your pins look fantastic and allow them to be re-pinned over and over.