Announcement Size Mixed Media Cards This small card is ideally suited for formal announcements, gift enclosures, invitations, change of address and thank you notes. Announcement Size envelopes are 3.625" x 5.125". Announcement cards meet domestic size requirements for US 1st Class Mail. Full Size Mixed Media Cards These larger size cards can be used to design a greeting for any occasion from birthdays, holidays and invitations to general correspondence. Full Size envelopes are 5.25" x 7.25". Slim Size Mixed Media Cards These cards are sized to fit into a #10 envelope and are perfect for greetings and correspondence. Slim Size envelopes are 9.5" x 4.125".