etsy - shipping costs

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hi grrls,
i guess this question is rather weird, but how do you calculate the shipping costs for your etsy items?
because i've seen that they vary a lot.
for example, different sellers selling (almost) the same item, it ranges from 3 to 5 dollars (to my country). which i think is a lot. considering that they should weigh the same!
so here's my question to experienced etsy sellers: how do you decide on how much shipping you'll charge for your items?
it does seem rather laborious to weigh every single item and then check for each at the post office how much shipping would be to this that and the next country.
thanks in advance for your answers!
♥