Instead of buying packages of mailing envelopes, consider making your own using only a piece of A4 (letter-size) paper. Not only is it a fun and easy paper project, but it will save money and allow you to make a custom-sized envelope for a card you want to send. There are, of course, several ways you can fold a homemade envelope, and not all will look like a traditional envelope.
To make an envelope for a card, lay the A4 paper horizontally on a flat surface.
Place the finished card on top of the paper, directly in the center. The card's long sides should be parallel with the paper's short sides.
Fold and crease the paper inward along its long sides (top and bottom). Leave a small amount of room on each side of the card.
Fold in the left side of the paper inward against the edge of the card, creating the bottom of the envelope.
Fold the other side of the paper inward to create the envelope flap.
Crease each side. Place a piece of tape or a decorative sticker on the edge of the flap to seal the envelope.
Turn over the envelope. Address it, stamp it and send the mail on its way.