#9 Envelope Size for Return Mail & Business Correspondence

The #9 envelope size (3 7/8" x 8 7/8") is widely used in business for mailing purposes. These envelopes fit perfectly inside #10 envelopes, making them the ideal solution for return mail, inserts, and payment collection. Whether you’re sending invoices, business correspondence, or direct marketing materials, #9 envelopes offer a compact yet effective way to handle important communications.

Dimensions: 3-7/8" x 8-7/8", Max. Enclosure Size: 3-5/8" x 8-5/8"