Cropping to a Specific Size
If you would like to crop to a specific size with the Crop tool (C), enter the dimensions and resolution you would like in the tool options up in the Options Bar. When you click-and-drag out your crop border, you will automatically constrain the crop handles to the size that you have set.
This is one of my favorite PS features. I used to wrestle with cropping in Image Size, but no more. Thanks for the post!