Calculated shipping doesn't factor in quantities greater than 1?

[leefrankis]

Hello,

I'm trying to set up calculated shipping rates. I cannot figure out how to set it up so that when a customer buys more than one item (of the same product) the size and weight of the package adjusts accordingly. 

Example

1 x product

package size = 19 x 14 x 2cm

package weight = 150g

2 x product = 19 x 14 x 4cm

package weight = 300g

I can set this up for fixed rates, but for calculated i cannot work this out, can anyone help please!