After wasting a lot of time and paper following the measurements on my WRMK Envelope Punch Board (which, so I was told by an SU demonstrator, is the same board as SU's) and the web site http://www.thecraftyowl.co.uk/EnvelopeExpert
I came up with correct measurements for the four sizes of cards I use the most: 4-Bar (3-1/2x5), A2, A6 and A7. After reading a thread about this subject, I used The Crafty Owl's measurements for an A2 card with 1/8" all around. I entered 4-1/2" x 5-3/4", and was told to use an 8-3/8" square piece of paper with the score at 4-5/8". Following that formula yielded an envelope that measured 4-3/4" x 6"! Too big.
Here are the formulas I came up with, and remember, the envelopes have an extra 1/8" all around.
4-Bar: 7-1/8" square paper, score and punch at 4-1/8"
A2: 8" square paper, score and punch at 3-9/16"
A6: 8-7/8" square paper, score and punch at 5"
A7: 9-3/4" square paper, score and punch at 5-5/8"
The envelope punch board makes it easy to make your own envelopes, but you need the right formulas and the correct envelope sizes. Look at your board for the A-2 card size, which should be 4-1/4" x 5-1/2", and you'll see it listed as 4-1/2" x 5-1/2". The card sizes for A6 and A7 are incorrect as well. Craft tool companies, are you reading this? Can some company please make a board that lists correct card sizes and formulas for 1/8" margins on all sides?!