No, you do not have to know what the weight is of your metals. Now, it would be good to have an idea, so that way, you can Fed X, instead of paying the shipping yourself, plus paying for insurance and or confirmation of delivery via USPS. That said, if you are more certain than not, that your metal weighs at least one troy ounce, then ship it via Fed X. USGoldBuyers will pay for it. They have an account with them. To give you an idea as to what that feels like, take 6 US quarters and put them in your hand. It might not seem like all that much, but it takes quite a bit of metal to be appoximately equal to that example. And again, that is an approximation.