Depends on what you're using to work with your pics. Cropping uses a ratio... think in terms of the rise and the run from your math classes (I can't remember...that may have been trig or calculus... I suck at math). 16:9, for example, means for every 16 units wide a picture is, it's 9 units tall. So a picture that's 160 pixels by 90 pixels will have the same height/width ratio to one that is 320 by 180.
In photo shop you can use a fixed aspect ratio to crop, then go in to set the photo size. If you're using a consistent aspect ratio, setting the same width with constrained aspect ratios will always give you the same height.
If you're not using photo shop, I'm not sure what to tell you.
and yes, guys, I'm still here. I lurk painfully little anymore, and I never get to comment...
I just thought I might be of help here.
Great start to your PN, too. Keep it up.