Custom crop (specific size required)

I'm very new to Lightroom and having trouble with some basic tasks.  I have an interest in cropping to a specific size.  It's not one of the offered sizes in the crop tool and with custom I don't see any way to determine crop size in either inches or pixels. so, 2 questions

1) how do I tell the size of my cropped image while cropping it?

2) Is it possible to use my completed crop as one of the offered sizes for my future use?

{Title edited by Moderator for clarity and to aid search queries}