Invitation sizes are standard sizes that are used for various types of invitations. These sizes are designed to fit in standard envelopes and to go well with different types of events.
Average sizes range from 3 1/2 by 5 inches to 5 by 7 inches. Different invitation sizes imply different functions. A 3 1/2-by-5-inch invitation sheet, for example, is typically used as an RSVP card and is paired with a larger invitation, often 5 by 7 inches, to a large, formal event such as a wedding. A 4-by-6-inch invitation is used for celebrations such as birthdays, graduation parties and other similar events.