The strongest pick for most senders is a folded A7 card, roughly 5 by 7 inches, with a blank interior and a matching rectangular envelope. It wins on five criteria: writing room, mailing cost at standard first-class rates, keepsake quality, range of designs, and how well it handles a photo or a small enclosure.
Folded A7 card with a blank interior
A7 is the common 5 by 7 inch folded format. The front carries the artwork, the inside is empty, and the paper weight is usually heavy enough to take gel pen or fountain ink without bleed through. The envelope is rectangular, which keeps it inside normal sorting.
Pros
- Blank interior gives space for a real note, not just a signature.
- Rectangular envelope in a standard size mails with a first-class stamp in most cases.
- Enough surface for a themed design, a name, or a date.
- Folded spine and heavier stock make it feel like something worth keeping.
Cons
- Costs more per card than a boxed multipack.
- Too large for a gift tag or a small card holder on a bouquet.
- A blank inside asks more of the sender than a printed verse.
Best for the main card you send to the parents, and for anyone who wants to write a paragraph rather than a line.
Flat 4 by 6 inch photo card
These are printed on one side or both, often with a photo of the baby, the parents, or a sonogram. They are sturdy, single sheet cards rather than folded ones.
Pros
- Photo carries the message when words are hard to choose.
- Cheap to order in small batches and quick to personalize.
- Fits standard photo frames, so it can go on a shelf later.
Cons
- Little room to write, especially if the back is printed.
- Feels less formal than a folded card for grandparents or close friends.
- Photo quality depends on the image you supply.
Best for a wide send list: coworkers, neighbors, and casual friends.
Square 5.5 inch card
Square cards look modern and photograph well. The catch is the envelope. In the US, square envelopes generally count as non-machinable and can need extra postage, so budget for that if you are mailing many of them.
Pros
- Distinctive shape that stands out in a stack of mail.
- Often printed on thick cotton stock with a clean, minimal design.
- Works well for a short, bold message.
Cons
- Extra postage is common.
- Fewer off-the-shelf designs than standard rectangular sizes.
- Harder to frame, since square frames are less common.
Best for a design minded friend who will notice the paper and the shape.
Boxed set of small cards
Boxed sets usually hold 8 to 20 small cards with matching envelopes, often in a 3.5 by 5 inch or 4 by 5.5 inch size.
Pros
- Lowest cost per card, which matters when you are writing to a whole team.
- Handy to keep at a desk for the next arrival.
- Small size suits a few warm sentences.
Cons
- Designs repeat, so the card says less about the specific family.
- Small panels fill up fast.
- Paper quality varies a lot between sets.
Best for an office, a club, or a group gift where several people sign one card each.
Letterpress or foil stamped card
Letterpress and foil cards use a pressed or metallic finish on heavy cotton paper. They are the most tactile option and the most expensive.
Pros
- Texture and depth that flat printing cannot copy.
- Strong keepsake value for a first grandchild or a long awaited arrival.
- Usually sold in small runs, so the design feels less common.
Cons
- Highest price per card by a wide margin.
- Longer production and shipping times.
- Thick stock can push an envelope over the weight limit if you add extras.
Best for grandparents, godparents, or anyone you want to honor with the nicest card in the pile.
Mailing and wording checks
- Weigh a filled envelope if you add a photo, a bookmark, or a gift card. Extra weight can change the postage.
- Write the parents' names, not just the baby's, and mention the baby by name once you know it.
- Keep the message short but specific: a due date joke, a trait you hope the baby inherits, or an offer of a meal.
- Sign with your full name if the parents may not recognize your handwriting.
One practical habit: buy two of the card you like. The second one sits in a drawer until the next arrival, and you skip the last minute trip to the shop.