When you have important documents, papers or other materials that need to be mailed, a 9-inch by 12-inch envelope is an option. Nine- by 12-inch envelopes are a good choice when the documents you're sending cannot be folded in order to be placed in a business envelope or if, when folded, the documents are still too large for a regular-sized envelope. In order to make sure your envelope arrives safely to its recipient, it's important to make sure you meet postal requirements.
Determine which type of 9-inch by 12-inch envelope is appropriate for you. If you're mailing something that should not be bent or may be fragile, a padded envelope would be best.
Place your document or item in the envelope and ensure the filled envelope isn't more than 3/4-inch thick, as required by the post office.
Address your 9-inch by 12-inch envelope by placing the mailing address in the center and the return address in the upper left corner on the same side as the mailing address.
Bring the 9-inch by 12-inch envelope to the post office so it can be weighed on a postal weight scale to determine postage needed.
Items you will need
9-inch by 12-inch envelope
Many post offices have self-serve areas available 24 hours per day that allow you to weigh and purchase postage for a 9-inch by 12-inch envelope being sent within the United States.
When sending a 9-inch by 12-inch envelope to another country, purchase postage from a postal clerk; an item with insufficient postage may take weeks to get back to you.
If your envelope ends up being more than 3/4-inch thick, you'll have to send the contents in a box, instead.