I take an 8.5 x 11 and cut it in half. So that would be a 4.25 x 5.5. Then I buy invitation envelopes from Staples Business Depot. They are 4 3/8 x 5 3/4.
HTH
Catherine
Like Catherine said, you can just cut standard cardstock in 8 1/2 x 11 to 2 4 1/4 x 5 1/2. Much easier, less scrap, and you can make card bases in bulk because you're not using up the more expensive 12x12 scrapping cardstock. I get my cardstock and the envelopes both at Walmart. I think for a ream of the 8 1/2 x 11 cardstock, its maybe $4 and for a pack of the card size Catherine mentioned called Invitation Envelopes you pay $3.50 for a pack of 60.
