One of my students asked how to make envelopes for odd sized cards. Here's a easy way to make an envelope for any size card.
All envelopes using this method begin with a square piece of paper. The size of the paper will be determined by the size of the card. In this example, the card size is 5 ½” x 4 ¼” and the envelope paper is 8” square. Here’s how to determine the size of the paper you will need. Trim a piece of 8 ½” x 11” paper to 8 ½” x 8 ½”. Lay the paper on the table diamond shape and place the card in the center of the diamond. Measure the distance from all four points of the card to the edge of the envelope paper. They should all be equal and ideally ½” from the point to the edge. If the paper is too large, trim it a bit until you get to the ½” distance at all four points. If the paper is too small, start over with a larger piece of paper. 12 x 12 scrapbooking paper works well.
Begin folding the points of the diamond over the card starting with the bottom, followed by the two sides. Use a pencil to print a small “T” (for top) on the last flap and fold it down. Open the paper and press flat. Using scissors, trim away the four small triangles made by the folding process as shown. Place the card inside the envelope to see that it fits. Fold up the bottom flap and glue the two sides. Fold the left and right flaps down onto the glued bottom flap and press to close. Trim away or fold down the tip of the bottom flap as shown. Erase the penciled T and fold down the top flap. Glue if desires.
Now you can make an envelope for any odd sized card as long as you remember the ½” rule.