Can't see what size my customers ordered

I have just started selling on Amazon and I listed a load of gemstones in different sizes. Customers can choose the size they order, but when I get the notification of a sale, I can’t find out what size they chose, I can’t see it on the packing slip or anywhere. So where do I look to find this out? and shouldn’t this be on the packing slip so the customer can get a confirmation?