Looking up and adding the values fixing different criteria

Hello,
"A column" the name of items such as Tiles, Pipes, Tables etc (many times repeated)
"B Column" the size of each item such as 10mm, 20mm, 50mm etc (i.e. tiles may be 10mm, 20 mm, 50mm, and the sizes can be repeat)

"C column" is the quantity of each item of each size.
The file has many cells/values.
Now I want to add in different column of each of the item of each size(i.e. tiles of 10mm how many quantity, tiles of 20mm how many quantity etc)