C4 paper size
229 × 324 mm
9.02 × 12.76 inches · 22.9 × 32.4 cm · aspect ratio 1:1.41
C4 size is 229 × 324 mm. Those are the C4 dimensions a printer works to; the same sheet in centimetres, inches, points and pixels is below.
What C4 is for
The C series exists for one reason: C(n) is sized to hold A(n). C4 at 229 × 324 mm takes an unfolded A4 sheet, which makes it the envelope for anything that must not be creased — certificates, contracts, photographs. C4 envelopes are usually sent as large letters rather than standard letters, which costs more postage in most countries.
C4 dimensions in every unit
| Unit | Width | Height |
|---|---|---|
| Millimetres | 229 mm | 324 mm |
| Centimetres | 22.9 cm | 32.4 cm |
| Inches | 9.02 in | 12.76 in |
| Points (PostScript) | 649 pt | 918 pt |
C4 in pixels
Pixel dimensions depend entirely on the resolution you are working at — there is no single "pixel size" for a sheet of paper. C4 size in pixels has every resolution, with file sizes and canvas setup.
| Resolution | Pixels | Use |
|---|---|---|
| 72 DPI | 649 × 918 | Screen preview only — far too coarse to print |
| 150 DPI | 1352 × 1913 | Draft printing, internal documents |
| 300 DPI | 2705 × 3827 | The standard for commercial print |
| 600 DPI | 5409 × 7654 | Fine detail, line art, archival scanning |
Setting up a print document? Use 300 DPI and add 3 mm of bleed on every edge unless your printer specifies otherwise.
How C4 relates to the rest of the series
C4 is C0 halved 4 times. Halving a sheet across its longer side is what generates the next size down, and because the sides are in a 1:√2 ratio the proportions survive every fold — which is the entire reason the series exists.
That makes 16 sheets of C4 exactly one sheet of C0, with nothing left over. The area works out at 0.0625 m², since C0 is defined as one square metre.
Scaling to the next size up or down is a factor of √2 ≈ 1.414 on each edge, so enlarging C4 to the next size is 141% on a photocopier and reducing it is 71%. Those two numbers are on the preset buttons of most copiers for exactly this reason, and they are the same for every size in the series.
About C4
The envelope that takes an unfolded A4 sheet. The C series exists precisely so that C(n) holds A(n).
Other ISO C series sizes
| Size | Millimetres | Inches |
|---|---|---|
| C5 | 162 × 229 mm | 6.38 × 9.02 in |
| C6 | 114 × 162 mm | 4.49 × 6.38 in |
| DL | 110 × 220 mm | 4.33 × 8.66 in |
| C3 | 324 × 458 mm | 12.76 × 18.03 in |
| C7 | 81 × 114 mm | 3.19 × 4.49 in |
Frequently asked questions
What size is C4 in mm?
229 × 324 mm.
What size is C4 in inches?
9.02 × 12.76 inches.
What size is C4 in pixels?
There is no single answer — it depends on resolution. At the print standard of 300 DPI it is 2705 × 3827 pixels; at 72 DPI it is only 649 × 918.