# Percentage in matrix colum grouped

Hello. I’m starting in the ssrs 2019
My question is about the a calculation of a percentage in matrix column.
I want calculate the percentage of a column in matrix, but grouped first by one column, and then the percentage over the main column.
In the following example, the column qty shows the quantity of the product1 in each storage, and the column qty_P shows percentage of the value over the total of product1, not over the total of the products.
For instance for the Product1 the qty_p has a total of 100% and the same for product2….etc
I know how to calculate the % over the total products, but don’t see a way to calculate the % over the segment product1, I mean what is shown in column qty_P

Product__storage__qty__qty_P
-----------+-----------+-------+-----------+
Product1--Magasin1--5-----10%
-----------+-----------+-------+-----------+
--------------Magasin2--20----40%
-----------+-----------+-------+-----------+
--------------Magasin3--25----50%
-----------+-----------+-------+-----------+
Product2--Magasin1--15----30%
-----------+-----------+-------+-----------+
--------------Magasin2--25----50%
-----------+-----------+-------+-----------+
--------------Magasin3--10----20%
-----------+-----------+-------+-----------+

Tried this and many others for the qty_p but doesn’t work (i know how to turn it into % just would like to know the calculation)
=Count(Fields!qty_p.Value ) / Count(Fields!qty_p.Value, "Product" )

If you could help I would really appreciate
Thanks