I have seen a Petal shaped Die for the big shot which makes a fixed size card/envelope, I don’t have that particular die and also would like to have various sizes of such an envelope for my square cards so I made myself a template.
This video shows what size cards the envelopes hold when they are printed on the sizes of paper I use most often. I re-sized the templates as large as possible on each size of paper by reducing the margin to the minimum setting in Word. A 6″ x 6″ sheet will give you an envelope that holds a 3″ x 3″ square card, a 8″ x 8″ will produce an envelope which will hold a 4″ x 4″ size card and an A4 sheet (which is a standard letter size piece of paper or card) will make an envelope that holds a 4.5″ x 4.5″ card or if you follow the instructions in the video will also hold a CD or DVD. The instructions given to help fit the CD can also be used if your card is slightly too large or has alot of dimension.
Here is your template:
(click on the image to expand before saving to your computer)