The 5.5 × 4.25 in bi-fold
A half-letter sheet folded once across the middle — a small landscape cover and back, opening to a full 5.5 × 8.5 in page inside.
Closed size5.5 × 4.25 in
Opens to5.5 × 8.5 in
FitsA2 envelope
FilesLayered PSD, smart objects
That closed size is the standard American card format, the one blank card stock and A2 envelopes are cut for, and it puts the piece in different company: invitations, save-the-dates, thank-you notes, RSVPs, small menus, gift and loyalty cards, place settings. It reads as something kept rather than handed out, which is most of the reason to fold a sheet this small in the first place.
The cover is where the work is. There's room for a name, a date and one image, so it has to run on a single element rather than a layout — this is the format that punishes a busy cover fastest. Inside, the crease sits across the middle rather than down the side, so opening it gives you a tall page rather than a wide spread, and artwork can run from top to bottom across both halves as one image.
Folded and set upright it also stands on its own, which is why the same shape works as a table tent or a counter card — worth checking the back panel actually says something, because on a table it's facing half the room.
In the sets: closed on the cover, standing and open flat from above, so you can present the card and the full inside together. Each is a layered PSD with smart objects — the artwork sits on its own layer, so replacing it leaves the fold, lighting and shadow untouched.