Crop to Size
Use the cropping tool in Photoshop to determine the physical size and resolution of an image.
When you select the cropping tool, specifications will appear at the top of the screen.
Enter size in inches (X in) or picas and points (XpX) and resolution in pixels per inch.
As you drag across the image, the aspect ratio (height to size) will stay consistent. You may rotate the image.
Layers will remain unchanged.
If you save at this point, the cropping is final. If you want to save both versions, be sure to save before you crop and then do a Save As with another name for the cropped image.