This app was mentioned in 2 comments, with an average of 5.50 upvotes
Lots of these seem quite unrealistic if the goal was to be simple.
My suggestion is a simple, material themed, barbel calculator.
What I am using right now is https://play.google.com/store/apps/details?id=byscut.weightplater&hl=en and while it works well, it is ugly as fuck.
That is my suggestion to you OP. Hopefully you can come up with something.
W8r Pl8r free barbell plate calculator.
https://play.google.com/store/apps/details?id=byscut.weightplater
Dumb name, good app.