How do you calculate the number of sellers per product category using tableau in this example I have categories and the number of sellers in each category I also have a reference line showing the average of those let’s add new sheet and see how to do this in tableau Let’s start by moving category to rows in writing the calculation so if I create a new calculated field and call it count of seller count D of seller. Click apply Click apply okay we’ll put that count into the view. I get a bar chart of the number of sellers per category if I want to calculate an average of these three I’m going to use a level of detail calculation and create a calculated field call it average count of seller I’m going to fix the count at the category level so for each category count the sellers. Click apply okay. Let’s move that over to detail and set it as average. Now I can right click the axis add a reference line and add the average sales.