Shipping Rules - Add the size of an item
Add a size selection for each product. I went to set up shipping rules, however as I have some products that are the same weight but fall into different size categories (Large Letter & Parcel) When I set up shipping rules It will not be accurate. This is due to rules only taking into account of weight and order value.
This functionality is already present. You can choose between Letter, LL and Parcel already and set up rules for each.