Should I use packaged dimensions and weight for products?

I'm having a bit of trouble understanding what to put for my item weight and dimensions. Should this simply be the item itself or what the item would be when shipped? Obviously the packaging and weight would change when a customer buys more than one item.

So for example if one product on my site is 4oz but packaged it's 8oz, should I use the packaged or unpackaged weight within my product info?