If you make a card, providing it isn’t a postcard, an envelope is something everyone needs to go with it. You can purchase envelopes in standard sizes; the #10 which is 4 1/4 X 9 1/2 and is used in most businesses for letterhead, invoices etc. Then there are the A2 (4 3/8 X 5 3/4 ) and A7 (5 1/4 X 7 1/4) which I commonly use for my greeting cards.
Sometimes i get carried away and end up making a card without looking for an appropriate envelope size first, then I have to make my own. There are plenty of tutorials online on how to make them. I bought a envelope maker from Stampin’ Up and absolutely love it. It is a little harder when you are working with paper that is longer than the envelope maker but I am very careful when I run off the edge so as not to rip a hole in it. It isn’t expensive either. Making your envelopes is fun, you can use your own paper and color coordinate them to your projects. With my Cricut I can make envelopes with matching liners. Most of the cartridges have the availability. Wild Card has some very cool envelope and card designs.
I previously posted a post on how to used the Martha Stewart scoreboard. click on the link and it will take you there.
Here is a jpeg of an envelope type and size spec sheet. I hope you can read it. I’d attach a pdf of it, but don’t know how. Sorry. If you know how to include and attachment, let me know.