I personally use a set of scales to weigh and a tape to measure all my items, then logon to my shippers site and key in the stats for an accurate quote.
If the items are small enough, I always include an international shipping option at cost price to cover as much of the market as possible.
I haven't really taken the time to look at my stats, but I would take a guess and say that the international orders make up less than 10% of my online selling business, but like I said, I like to cover as much as the market as I can to maxmise my chances of a sale.