Nine- by 12-inch envelopes come in padded and unpadded varieties.
Nine- by 12-inch envelopes come in padded and unpadded varieties.

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.

An overstuffed envelope may end up ripping.
An overstuffed envelope may end up ripping.

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.