Choosing the right C envelope size can feel confusing with so many options available. The C series envelope system ranges from tiny C10 envelopes to poster-sized C0, each designed to fit specific paper dimensions perfectly.

I break down all C series envelope sizes with exact measurements in millimeters, inches, and other units. You’ll learn which paper fits in each envelope and how to select the right size for your mailing needs.

What are C Envelope Sizes?

The C envelope series follows the ISO 269 international standard for envelope dimensions. These envelopes work specifically with A and B series paper sizes used worldwide.

C envelopes sit perfectly between A and B series measurements. The area of any C envelope equals the geometric mean of the matching A and B paper sizes. For example, a C4 envelope is larger than A4 paper but smaller thanB4 paper.

Each C size envelope maintains a consistent aspect ratio of 1:√2 (approximately 1:1.4142). This mathematical relationship ensures that folded paper fits neatly without wasted space or awkward proportions.

The sizing system makes perfect sense once you understand the pattern. Each consecutive C size measures exactly half the area of the previous size. C5 is half of C4, C6 is half of C5, and so on down the line.

C Envelope Sizes Chart: Dimensions from C0 to C10

Here’s a complete breakdown of every C envelope size with precise measurements across multiple unit systems:

Most Common C Envelope Sizes and Its Uses

The C4, C5, and C6 envelope sizes dominate everyday use across offices and mailing centers. These three formats handle approximately 85% of standard correspondence needs.

DL envelopes represent the most popular business envelope format worldwide. The DL size (110 × 220 mm or 4.33 × 8.67 inches) closely matches the US #10 business envelope and fits standard business letters folded into thirds.

C7/6 envelopes offer a unique slim format that’s perfect for checks, compliment slips, and narrow documents. This size doesn’t follow the standard halving pattern, instead combining C7 width with C6 length.

C Envelope and Paper Compatibility: What Fits Where

Understanding which paper fits in which C envelope eliminates guesswork and wasted materials. The system follows a simple mathematical relationship designed for perfect compatibility.

C0

C0 envelopes (917 × 1297 mm / 36.1 × 51.1 inches) accommodate unfolded A0 paper sheets perfectly. These massive envelopes also hold B0 paper folded once along its length.

C1

A C1 envelope measures 648 × 917 mm (25.5 × 36.1 inches) and holds A1 paper unfolded. You can also fit A0 paper folded once or B1 paper with a single fold.

C2

C2 envelopes (458 × 648 mm / 18.0 × 25.5 inches) perfectly fit unfolded A2 paper. A1 sheets folded once also slide in comfortably, along with B2 paper folded once.

C3

The C3 envelope measures 324 × 458 mm (12.8 × 18.0 inches) and accommodates A3 paper unfolded. This size also holds A2 paper folded once or B3 sheets with a single fold.

C4

What size paper fits in a C4 envelope? A standard C4 envelope (229 × 324 mm / 9.0 × 12.8 inches) holds unfolded A4 paper perfectly. This is the most common office paper size worldwide.

C5

C5 envelopes measure 162 × 229 mm (6.4 × 9.0 inches) and hold A4 paper folded once along its length. A5 paper fits unfolded in C5 envelopes, making this a versatile mid-size option.

Are C5 and A5 the same size? No, C5 envelopes are slightly larger than A5 paper to provide proper fit. The envelope measures 162 × 229 mm while A5 paper is 148 × 210 mm.

C6

A C6 envelope (114 × 162 mm / 4.5 × 6.4 inches) accommodates A4 paper folded twice or A5 paper folded once. Unfolded A6 cards and postcards also fit perfectly.

C7/6

C7/6 envelopes measure 81 × 162 mm (3.2 × 6.4 inches) with an unusual slim profile. This format holds A5 paper folded lengthwise or serves as an alternative to DL envelopes for narrow documents.

C7

C7 envelopes (81 × 114 mm / 3.2 × 4.5 inches) fit A7 paper unfolded or A6 paper folded once. These small envelopes work well for tiny notes and gift enclosures.

C8

A C8 envelope measures 57 × 81 mm (2.2 × 3.2 inches) and holds unfolded A8 paper or A7 folded once. This miniature format suits very small items and documents.

C9

C9 envelopes (40 × 57 mm / 1.6 × 2.2 inches) accommodate A9 paper unfolded or A8 folded once. These tiny envelopes servespecialized purposes in various industries.

C10

The smallest standard size, C10 envelopes measure 28 × 40 mm (1.1 × 1.6 inches) and hold A10 paper unfolded or A9 folded. These micro envelopes have niche applications.

DL

DL envelopes (110 × 220 mm / 4.33 × 8.67 inches) represent the standard business envelope format worldwide. They hold A4 paper folded into thirds horizontally, creating the classic business letter format.

Choosing the Right C Envelope Size: Practical Applications & Tips

Selecting the correct C envelope size depends on your document type, folding preferences, and mailing costs. Each format serves specific purposes in business and personal correspondence.

C10 and C9 Envelope Uses

C10 envelopes (28 × 40 mm) work perfectly for seed packets, tiny labels, and miniature product samples. Craft supply stores use them for beads, sequins, and small embellishments.

C9 envelopes (40 × 57 mm) hold business cards cut in half, small gift tags, and jewelry findings. Electronics hobbyists store resistors, LEDs, and other components in this size.

C8 and C7 Envelope Applications

C8 envelopes (57 × 81 mm) accommodate trading cards, small photographs, and ticket stubs. Collectors appreciate this size for organizing memorabilia without bulky storage solutions.

C7 envelopes (81 × 114 mm) serve wedding invitation RSVP cards, gift card holders, and small greeting cards. The compact size keeps mailing costs minimal while maintaining professional presentation.

C7/6 Envelope Practical Uses

C7/6 envelopes (81 × 162 mm) provide the perfect slim format for checks, payment vouchers, and banking documents. The elongated shape prevents checks from folding awkwardly or getting damaged.

Businesses include compliment slips and discount vouchers in C7/6 size envelopes. The unique dimensions stand out in mailboxes, increasing the likelihood recipients notice promotional materials.

C6 Envelope Common Applications

C6 envelopes (114 × 162 mm) dominate the greeting card industry worldwide. Birthday cards, thank you notes, and holiday greetings typically use this popular format.

C5 Envelope Everyday Uses

C5 envelopes (162 × 229 mm) handle standard business letters when you want to fold A4 paper once. This creates a more compact mailing package than unfolded C4 envelopes.

Marketing teams use C5 size for brochures, sales sheets, and promotional materials. The format balances visibility with reasonable postage costs for direct mail campaigns.

C4 Envelope Professional Applications

C4 envelopes (229 × 324 mm) ship legal documents, contracts, and certificates without any folds. Important papers arrive crisp and professional-looking, ready for immediate use or framing.

Photographers send 8×10 inch prints in C4 envelopes with protective cardboard backing. The size prevents bending during shipping while maintaining competitive postage rates compared to larger formats.

C3 Envelope Specialized Uses

C3 envelopes (324 × 458 mm) work excellently for presentation materials, awards, and diplomas. Educational institutions mail transcripts and certificates in this size to ensure documents remain flat.

C2, C1, and C0 Large Format Applications

C2 envelopes (458 × 648 mm) handle architectural drawings, engineering plans, and large-format photography. The size accommodates A2 posters and graphics for retail displays.

C1 envelopes (648 × 917 mm) ship oversized artwork, technical blueprints, and trade show graphics. Design firms use this format for client presentations and portfolio pieces.

C0 envelopes (917 × 1297 mm) represent the largest standard size for massive posters, banners, and architectural renderings. These specialty envelopes typically require custom ordering and higher shipping costs.

DL Envelope Business Standard

DL envelopes remain the global standard for business correspondence, invoices, and statements. Nearly every office environment stocks DL size as their primary mailing envelope.

The DL format (110 × 220 mm / 4.33 × 8.67 inches) closely matches US #10 envelopes, making it familiar to American businesses conducting international correspondence. Window versions show addresses perfectly when letters fold correctly.

Mailing Cost Considerations

Smaller C envelopes (C6, C7, DL) typically qualify for standard letter postage rates in most countries. This makes them economical for bulk mailings and regular correspondence.

Larger formats (C4, C3, C2) often incur higher postage fees based on weight and dimensions. Always verify postal regulations before mailing bulk quantities to avoid unexpected costs.

Where to Buy C Envelopes in the USA

Office supply retailers like Staples, Office Depot, and Amazon carry common C envelope sizes including C4, C5, C6, and DL. Availability of smaller or larger sizes varies by location.

Online specialty suppliers such as PaperPapers, JAM Paper, and EnvelopeMall stock complete C series ranges. These vendors often provide bulk discounts and custom printing options for business needs.

International stationery importers offer authentic ISO-standard C envelopes manufactured to exact specifications. Quality varies significantly, so request samples before ordering large quantities for important mailings.

Window Envelope Options

Window C envelopes come in C4, C5, C6, and DL sizes with transparent panels showing recipient addresses. These eliminate manual addressing and reduce processing time for bulk mailings.

Position your address block 55mm from the left edge and 15mm from the top for standard window envelopes. This ensures addresses display correctly regardless of slight paper positioning variations.

FAQ’s (C-Envelope Sizes)

What size paper fits in a C4 envelope?

A C4 envelope (229 × 324 mm or 9 × 12.8 inches) fits unfolded A4 paper perfectly. The envelope also accommodates A3 paper folded once, B4 sheets folded once, or multiple A5 sheets without folding.

What size is C paper?

C paper doesn’t exist as a standard paper size. The letter “C” designates envelope sizes only under ISO 269 specifications, not paper dimensions.

What size is a C3 envelope?

C3 envelopes measure 324 × 458 mm (12.8 × 18 inches). This size accommodates unfolded A3 paper, A2 sheets folded once, or B3 paper with a single fold.

What is C2 size? How big is C2 paper?

C2 is an envelope size measuring 458 × 648 mm (18 × 25.5 inches). C2 paper doesn’t exist in standard sizing conventions—only C2 envelopes.

What size is C size?

“C size” refers to the entire C series envelope range from C0 through C10, plus the DL business format. The term encompasses all ISO 269 standardized envelope dimensions.

The most common C sizes include C4 (9 × 12.8 inches), C5 (6.4 × 9 inches), C6 (4.5 × 6.4 inches), and DL (4.33 × 8.67 inches) for everyday correspondence and mailing.

Are C4 and A5 the same?

No, C4 and A5 are completely different sizes serving different purposes. C4 is an envelope measuring 229 × 324 mm (9 × 12.8 inches), while A5 is a paper size measuring 148 × 210 mm (5.8 × 8.3 inches).

A C5 envelope fits A5 paper, not C4. The C4 envelope holds unfolded A4 paper or multiple A5 sheets without folding.

Is C5 the same as A5?

C5 and A5 are not the same size. C5 envelopes measure 162 × 229 mm (6.4 × 9 inches), while A5 paper measures 148 × 210 mm (5.8 × 8.3 inches).

How big is a B5 envelope?

B5 paper measures 176 × 250 mm (6.9 × 9.8 inches) in the ISO B series.

Conclusion

C envelope sizes offer a complete mailing solution for every document type, from tiny seed packets to architectural blueprints. The standardized system ensures your papers always fit perfectly without guesswork or waste.

Understanding C series dimensions and paper compatibility helps you choose the right envelope every time.

Whether mailing business letters in DL envelopes or shipping certificates in C4 format, the ISO standard delivers reliable results worldwide.