How do you use a kitchen scale?

I understand that things weigh less after they are cooked, but when I am trying to figure out a serving size do I weigh things raw or once cooked?  For example I had a Stop and Shop English muffin for breakfast and I weighed it before I toasted it and it was 70g even though the packaging claimed it was 56g, so I weighed it again after I cooked it and it was about 60g.  So I am utterly confused.  I need advice.

Nutrition information are generally based on the the food 'as sold'.  So the 56g stated on the packet is 56g of uncooked muffin and is based on an average. The nutrition information on packets only has to be 80% accurate in any case

oh wow I never knew that.  Thanks for letting me know.