I used the Royal Mail website and weighed my boxes, and then I typed in the weights and I got a better idea of what to charge for my delivery prices.
I just thought I pop the link here to the Royal Mail calculator just in case any of you peeps need something to help you gauge prices. Also, see what your products can fit in to save space and money on packaging such as using letter envelopes for small jewellery
http://www.royalmail.com/business/services/sending/parcels-uk/1st-class-parcels