C series sizes: C0 to C10 for envelopes

The C series is made for envelopes and folders. Each C size is a little larger than the A size with the same number, so an A4 sheet (210 × 297 mm) fits a C4 envelope (229 × 324 mm), and an A5 sheet fits C5.

Updated 7 October 2026 by the editorial team

Contents of this page

C0917 × 1297 mm C1648 × 917 mm C2458 × 648 mm C3324 × 458 mm C4229 × 324 mm C5162 × 229 mm C6114 × 162 mm C781 × 114 mm C857 × 81 mm C940 × 57 mm C1028 × 40 mm DL110 × 220 mm C6/5114 × 229 mm

All C sizes with dimensions

C series under DIN 476-2
Size	mm	cm	inches
C0	917 × 1297 mm	91.7 × 129.7 cm	36.1 × 51.06 in
C1	648 × 917 mm	64.8 × 91.7 cm	25.51 × 36.1 in
C2	458 × 648 mm	45.8 × 64.8 cm	18.03 × 25.51 in
C3	324 × 458 mm	32.4 × 45.8 cm	12.76 × 18.03 in
C4	229 × 324 mm	22.9 × 32.4 cm	9.02 × 12.76 in
C5	162 × 229 mm	16.2 × 22.9 cm	6.38 × 9.02 in
C6	114 × 162 mm	11.4 × 16.2 cm	4.49 × 6.38 in
C7	81 × 114 mm	8.1 × 11.4 cm	3.19 × 4.49 in
C8	57 × 81 mm	5.7 × 8.1 cm	2.24 × 3.19 in
C9	40 × 57 mm	4 × 5.7 cm	1.57 × 2.24 in
C10	28 × 40 mm	2.8 × 4 cm	1.1 × 1.57 in

The principle: A fits C fits B

The C series sits exactly between A and B of the same number. In maths terms, C4 is the geometric mean of A4 and B4. The result is an envelope that takes an A4 sheet with just under 1 cm to spare on the short side and about 1.4 cm on the long side. A B4 envelope in turn takes a C4 envelope.

Contents	Envelope	Room per side (approx.)
A4 flat (210 × 297)	C4 (229 × 324)	9.5 × 13.5 mm
A5, or A4 folded once (148 × 210)	C5 (162 × 229)	7 × 9.5 mm
A6, or A4 folded twice (105 × 148)	C6 (114 × 162)	4.5 × 7 mm
A4 in thirds (99 × 210)	DL (110 × 220)	5.5 × 5 mm

The envelope finder works this out for any paper size and fold.

Which standard covers the C series?

Internationally, the C series was set out in ISO 269 until 2009, when that standard was withdrawn without a replacement. In Germany the C series is still defined in DIN 476-2 (2008 edition). Envelope details such as flaps, windows and special sizes like DL and C6/5 are covered by DIN 678, window positions by DIN 680. Outside Germany, C sizes remain in everyday use worldwide even without a current ISO standard.

C sizes beyond envelopes

Presentation folders and document wallets for A4 are often made in C4 so that the sheets do not stick out. C3 (324 × 458 mm) takes A3 plans flat. C2 and larger sizes are mostly seen in archive and plan folders.

Useful supplies

C4 envelopes

For flat A4 documents such as certificates or contracts. A board-backed version keeps sheets flat in the post.

View on Amazon*

C5 envelopes

For A5 booklets, brochures and A4 folded once. Peel and seal saves time when you post more than a handful.

View on Amazon*

C6 envelopes

For A6 greeting cards and A4 folded twice. At 114 × 162 mm it also goes as a standard letter in Germany.

View on Amazon*

C6/5 window envelopes

At 114 × 229 mm, slightly larger than DL. An A4 letter folded in three slides in more easily and still goes as a German standard letter.

View on Amazon*

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* Affiliate link: if you buy through this link, Amazon pays us a small commission. The price stays the same for you. As an Amazon Associate I earn from qualifying purchases.

Frequently asked questions

Which envelope fits A4 unfolded?

C4, which measures 229 × 324 mm.

How big is a C5 envelope?

162 × 229 mm. It takes A5, or A4 folded once.

How big is a C6 envelope?

114 × 162 mm, made for A6 or A4 folded twice.

Is DL a C size?

Not strictly. DL (110 × 220 mm) is a special envelope size for A4 folded into thirds.