How much must a flat weigh to meet mailing requirements?

To meet mailing requirements, a flat must weigh no more than 6 ounces. This weight limit is essential because flats, which include large envelopes and unmated cards, are subject to certain postal regulations that vary based on weight and size. If a flat exceeds this weight, it may need to be mailed as a different class or type of mail, which could incur higher postage costs or different handling procedures. Therefore, understanding the weight limitations is crucial for proper mailing practices.