I think you've made Christmas cards and are looking for envelopes to send. A8 Envelope Best suited for you. Here are the measurements for you.
Envelopes are still being used as a courtesy. My mom still uses envelopes when someone has to be paid. Looks for hours of envelopes. He spends hours working on it. She's nice.
There are different envelopes for different purposes. A8 Envelope Usually used to send you a Christmas card.
Given that the first Christmas cards were sent in the 1800s, this kind of dice has been around for quite a long time.
If you think size is matter here is the our sizes home pages