Need envelope size in for printing in Address Book

I just received in the mail the Christmas cards I designed in iphoto...they look great! I want to use Address Book to print the name and addresses of the recipients (as well as my return name/address)on the envelopes that came with the cards. The envelopes are 7.25 inches x 5.25 inches (for a 7x5 card...pretty standard), but I can't find these dimesions in the the drop-down envelope printing menu in Address Book. Any ideas? I guess I could set up a custom envelope but need to calculate the dimensions for the recipients as well as the return address. I assumed that iphoto cards/envelopes would match a printing option in Address Book...am I crazy?