C9 Paper Size

C9 is a format in the C series paper, and the C series paper is a series of commonly used papers in the ISO 216 international paper standard, the C series formats are geometric means between the B series and A series formats with the same number (e.g., C2 is the geometric mean between B2 and A2), it mainly used for envelopes. The width of the C9 paper is 40mm(1.6 inches) and the height is 57mm(2.2 inches).

Format/name	C9
Width(mm)	40 mm
Width(in)	1.6 inches
Height(mm)	57 mm
Height(in)	2.2 inches

Taking our commonly used credit cards as a reference, the size of the credit card is 85.6 mm x 53.98 mm (3.4 in X 2.1 in). The paper size of C9 format is approximately 0.5 times the width of the credit card and approximately 1.1 times the height of the credit card.

ISO 216 is an international standard is a universal standard all over the world except in North America (the United States and Canada) and parts of Latin America.

C Series Paper Size

Format	Width × Height (mm)	Width × Height (cm)	Width × Height (in)
C0	917 × 1297 mm	91.7 × 129.7 cm	36.1 × 51.1 in
C1	648 × 917 mm	64.8 × 91.7 cm	25.5 × 36.1 in
C2	458 × 648 mm	45.8 × 64.8 cm	18 × 25.5 in
C3	324 × 458 mm	32.4 × 45.8 cm	12.8 × 18 in
C4	229 × 324 mm	22.9 × 32.4 cm	9 × 12.8 in
C5	162 × 229 mm	16.2 × 22.9 cm	6.4 × 9 in
C6	114 × 162 mm	11.4 × 16.2 cm	4.5 × 6.4 in
C7	81 × 114 mm	8.1 × 11.4 cm	3.2 × 4.5 in
C8	57 × 81 mm	5.7 × 8.1 cm	2.2 × 3.2 in
C9	40 × 57 mm	4 × 5.7 cm	1.6 × 2.2 in
C10	28 × 40 mm	2.8 × 4 cm	1.1 × 1.6 in