About how much does a standard key weigh?

A house key is light as a feather ( lol ) you should need no more than a stamp or two. The question is how do you plan on mailing it out? in a padded envelope or a small box? this is where you are going to need to find out how many stamps you are going to need. Ask a post office for they can give you an answer. But a single key is really light. Good luck w/ sending it and may it get to it's desination safely.