Kojak: Here’s a Link to The Mouse Factory,
which I feel pretty much has their sizes and stages correct....
their pics show the different sizes and average weights as well.
Just scroll over the picture of any given size mouse/rat, and it
will tell you what it is. If you click on that particular rodent,
it will show it next to a ruler to give you a size reference.
And it shows how they are packaged of course.
Again, not a sales pitch or advertisement on my part,
it’s just the best picture demonstration I know right off hand.
Hope that helps.

wonder if a frozen rat weight more or less than alive