Count number of raw in a calculated column

Hi,

In my main calculated column I display % usage for my products. I have 4 categories that describe how much the products are used (ex. if %usage => 60 , average etc..).
I created a visualization that show the products and these 4 categories.

I want know to count the number of products in each category. How can I do this?
My goal in to create a stacked column chart, which display the number of products in each usage category

Thank you for the help