Featured Images Sizing – Post

I read the instructions and searched the web to find the standard image size of the Featured Image for a Post. I believe it is 644x320. I created a file to those specific dimensions. When I added it to a post, the theme automatically cropped it. I tried the various settings for the image size in the post, but all are still cropped. (Feature Slider was the closest to correct) What is the correct pixel size for the featured image so they are not cropped? http://beingvalued.com/home/2013/09/28/am-i-on-path/ Thanks!