On Etsy, I list my shipping as $2.95 and if they order multiple items it's $1.00 for each additional item. I have a scale that connects to my computer and weighs the package for me and tells me the postage. This particular package weighed a little over 10 ounces and shipping was $2.92. I really didn't have a clue on what to charge for shipping. I looked through other Etsy shops to see what others were charging for shipping and I went with the average of what I saw. When someone orders off of Etsy, like out of town friends, I send them a PayPal invoice with the exact shipping on it.
Can you tell me what scale you have and where you bought it?
I would LOVE to know one that hooks up to the computer!