ISO C series (envelopes)

C3 envelope size

C3 envelope measures 324 x 458 mm (12.76 x 18.03 in). Envelope for unfolded A3.

324 x 458millimetres

12.76 x 18.03inches

3,827 x 5,409pixels @ 300 dpi

Dimensions in every unit

Unit	Width x height
Millimetres	324 x 458 mm
Centimetres	32.4 x 45.8 cm
Inches (decimal)	12.756 x 18.031 in
Inches (fraction)	12 3/4 x 18 1/16 in
Points (1/72 in)	918.4 x 1298.3 pt
Picas	76.54 x 108.19 pc

Pixel dimensions by resolution

Resolution	Pixels	Megapixels
72 dpi	918 x 1,298 px	1.2 MP
96 dpi	1,225 x 1,731 px	2.1 MP
150 dpi	1,913 x 2,705 px	5.2 MP
200 dpi	2,551 x 3,606 px	9.2 MP
300 dpi	3,827 x 5,409 px	20.7 MP
600 dpi	7,654 x 10,819 px	82.8 MP

300 dpi is the usual target for printed photos and artwork; 72–96 dpi is screen resolution.

Document size with bleed

Bleed	Millimetres	Inches
3 mm bleed (each side)	330 x 464 mm	12.992 x 18.268 in
0.125 in bleed (each side)	330.4 x 464.4 mm	13.006 x 18.281 in

How many C3 envelope fit on a press sheet

Sheet	Without bleed	With 3 mm bleed
13 x 19 in (Super B)	1-up	1-up
B2 (offset)	2-up	2-up
B1 (offset)	4-up	4-up

Simple grid imposition with no gutters or gripper margin; real layouts may fit fewer.

The √2 system

C3 envelope has an aspect ratio of 1 : 1.4136 — close to √2 (1.4142). Folding or cutting it in half across the long side produces the next smaller size in the series with the same proportions, and two sheets side by side form the next larger size. This is why scaling between sizes in the series (for example on a photocopier) never crops or distorts the page.

Frequently asked questions

What are the dimensions of C3 envelope?

C3 envelope is 324 x 458 mm, which is 12.76 x 18.03 in (12 3/4 x 18 1/16 in).

How many pixels is C3 envelope at 300 DPI?

3,827 x 5,409 pixels at 300 dpi, or 1,913 x 2,705 at 150 dpi.

Sources & data

Dimensions per the relevant standard; see sources.