I have used your numbers and set them out in a table A1 to C6


I then set up a table with the possible sizes in the left hand column(A12 down)
and the possible product groups in the column headers in B11 and across

entered in B12

=SUMPRODUCT(--($C$1:$C$6=$A12),--($A$1:$A$6=B$11),$B$1:$B$6)

note the $ signs especialy for $A12 and B$11

this makes it possible to extend the formula down the columns and across

good luck