Wondering which standard card sizes to buy or cut? Two systems rule: metric A6 and C6 in most of the world, and US A2, A6 and A7 in inches.
This guide is part of our card making series.
| Item | Size |
|---|---|
| ISO A6 sheet (flat) | 105 × 148 mm |
| ISO C6 envelope | 114 × 162 mm |
| ISO DL envelope | 110 × 220 mm |
| US A2 folded card | 4.25″ x 5.5″ |
| US A7 folded card | 5″ x 7″ |
Figures come from Markus Kuhn’s ISO paper page and a printer’s FAQ on greeting cards. Sizes and naming can change or differ by maker, so check the source before you rely on them.
Why two sets of card sizes exist
Most countries outside North America use the ISO paper system. Every size is made by halving the one before it, so a sheet keeps the same proportions however many times you fold it.
North American card makers work in inches and use the labels A2, A6 and A7 for folded cards and their envelopes. The labels look like the ISO ones but describe different sizes, which is where most mix-ups begin.
So before you buy blanks or envelopes, check whether a listing is quoted in millimetres or inches. If it names “A6” with no unit, ask which system it means.
Metric card sizes and their envelopes
The ISO A-series gives you the sheet sizes. According to Markus Kuhn’s table, an A5 sheet measures 148 × 210 mm and an A6 sheet measures 105 × 148 mm, both in millimetres.
A5 folded in half gives you an A6 card, which is why A6 is such a common finished size. A card cut from A4 and folded once ends up at A5, a roomier option for big layouts.
The same page lists the matching C-series envelopes, which are a little bigger than the paper they hold:
- C6: 114 × 162 mm, a snug home for an A6 card.
- C5: 162 × 229 mm, for an A5 card or an A4 sheet folded once.
- DL: 110 × 220 mm, a long, slim shape for tall cards and letters.
- C4: 229 × 324 mm, for flat A4 sheets.
Kuhn’s page notes that for postal purposes, ISO 269 and DIN 678 define these envelope formats. The matching envelope is slightly larger than the card, but bulky decorations may require extra clearance.
US card sizes: A2, A6 and A7
In the US, a printer’s guide describes common folded sizes including A2 at 4.25″ x 5.5″ and A7 at 5″ x 7″. That guide calls A7 the industry standard and its safe default for most occasions.
- A2: 4.25″ x 5.5″, suited to short notes.
- A6: used for photo cards and mid-range designs.
- A7: 5″ x 7″, the size most people reach for on most occasions.
A smaller card feels personal and costs less to post in many places, while a larger one gives you space for layered dies, a big sentiment or a photo. Neither is better; the right pick depends on the design you have in mind.
If you sell or swap cards with friends overseas, state the sizing system and finished dimensions in your listing. A short line such as “folds to A6, 105 × 148 mm” saves everyone a guessing game and cuts down on returns.
Treat these as common trade sizes rather than a law. Some sellers quote slightly different numbers for the same label, and envelope dimensions run a little larger than the card inside.
Common mistakes with standard card sizes
The first mistake is cutting a card to the exact envelope size. With no breathing room, the card will catch on the flap or bend at the corners as you slide it in.
The second is relying on size labels without comparing the actual card and envelope dimensions and allowing clearance.
Last comes forgetting the fold. A folded A6 card starts life as an A5 sheet, so plan your cardstock purchase around the finished size, not the flat one.
- Leave a few millimetres of clearance around the card.
- Compare the card and envelope dimensions in the same units, allowing clearance.
- Measure the folded card, not the flat sheet.
- Check that squares and long shapes are accepted by your post office.
Reading the labels on cardstock and blanks
Cardstock is usually sold as flat sheets, while blanks are pre-scored and folded cards. A listing for a flat A5 sheet gives you an A6 card once you fold it, whereas a listing for an A6 blank is already the finished size.
That difference trips up many beginners. Always check whether the number describes the sheet before folding or the card after folding.
- Flat size: the sheet as it arrives, before any fold.
- Folded size: the finished card standing on a shelf.
- Envelope size: the outside dimensions of the closed envelope; allow clearance for the card inside.
Grain direction matters too. Folding across the grain can crack the surface, so score firmly along the fold and burnish it flat with a bone folder.
How to choose a size for your project
Start with the envelope, because that is the part that is hardest to change. Postal rules and what your shop stocks matter more than the exact card.
- Compare measurements in the same units, whether millimetres or inches.
- Pick the finished card size, such as A6 or A7.
- Buy envelopes that match, such as C6 for a metric A6 card.
- Cut your cardstock to twice the finished width, then fold.
- Test with one card and its envelope before cutting a stack.
Thick layers change the fit. Heavy extras such as dimensional toppers or heat embossing for card making can add bulk or leave a raised surface, so allow some room in the envelope.
Thinking about weight? A flat, simple card travels well in a standard envelope. A bulky card with buttons or ribbon may need a padded or oversized envelope and a different postage rate.
What if you can’t find the right envelope?
If a ready-made envelope is out of stock or does not fit an unusual card, you can make your own from patterned paper. Our walkthrough on how to make an envelope covers the method.
Measure the card first, then add a small margin on every side. Square and very small cards often need a custom envelope, and they can cost extra to post, so check your postal service’s rules before you commit.
Frequently asked questions
What is the most common metric card size?
Show answer
A6 is the most common finished size, at 105 × 148 mm when measured as a flat sheet, and it fits a C6 envelope at 114 × 162 mm.
Is a US A6 card the same as an ISO A6 card?
Show answer
No. A US A6 card has different dimensions from ISO A6, which is 105 × 148 mm. The labels match but the sizes do not.
Which envelope fits a DL card?
Show answer
A DL envelope, 110 × 220 mm, is the matching shape for long, slim cards.
Which US size is the safest default?
Show answer
The printer’s FAQ calls A7, at 5″ x 7″, the safe default for most occasions because its envelopes are easy to find.
