Reference library
C3 Envelope Paper Size
C3 measures 324 x 458 mm, 32.4 x 45.8 cm, or 12.76 x 18.03 in. See pixel dimensions by DPI, aspect ratio, bleed setup, comparisons, and related tools.
Last checked: 2026-05-01
How we calculate this
Methodology and source handling
We convert physical sizes to inches, multiply by the selected DPI/PPI value, and round to whole pixels.
Quick answer
Copy-ready answer
C3 is 324 x 458 mm, 32.4 x 45.8 cm, or 12.76 x 18.03 in. At 300 DPI, C3 is 3827 x 5409 px.
Dimensions and specs
| Millimeters | 324 x 458 mm | |
|---|---|---|
| Centimeters | 32.4 x 45.8 cm | |
| Inches | 12.76 x 18.03 in | |
| 300 DPI pixels | 3827 x 5409 px | |
| Aspect ratio | 1:1.4136 | |
| Standard family | ISO C Envelope Series |
Pixels
Pixel dimensions by DPI
| DPI / PPI | Width | Height | Use |
|---|---|---|---|
| 72 DPI | 918 px | 1298 px | Screen or draft reference density |
| 96 DPI | 1225 px | 1731 px | Screen or draft reference density |
| 150 DPI | 1913 px | 2705 px | Screen or draft reference density |
| 300 DPI | 3827 px | 5409 px | Common high-quality print setup |
| 600 DPI | 7654 px | 10819 px | High-resolution archival or print workflow |
Formula
How to calculate this size
324 mm x 300 PPI = 3,827 px wide.
Use this when the artwork stops at the finished edge.
Add 0 mm per side before calculating pixels when artwork reaches the edge.
Common mistakes
Avoid these c3 envelope paper size problems
A paper size needs a PPI target before pixels mean anything for print.
Portrait and landscape use the same dimensions, but width and height swap in the export.
Paper pages show trim size first; add bleed only when the design prints to the edge.
Calculator
Calculate pixels and bleed
Enter any DPI to calculate the pixel dimensions for this physical size.
Compare
Compare C3 Envelope Paper Size
Open a curated comparison or send both sizes into the compare tool with a fragment URL.
- C3 Envelope Paper Size
- 324 x 458 mm
- C2
- 458 x 648 mm
- C3 Envelope Paper Size
- 324 x 458 mm
- C4
- 229 x 324 mm
- C3 Envelope Paper Size
- 324 x 458 mm
- A4
- 210 x 297 mm
- C3 Envelope Paper Size
- 324 x 458 mm
- US Letter
- 215.9 x 279.4 mm
Workflow
Use C3 Envelope Paper Size in a finished file
Copy the millimeter, centimeter, or inch dimensions for the selected paper standard.
Use 300 PPI for most sharp print exports, or match the printer requirement.
Multiply inches by PPI, then add bleed only when artwork reaches the trimmed edge.
Related
Related pages and tools
Same branch
Nearby pages
FAQ
Common questions
What is the exact C3 size?
C3 measures 324 x 458 mm, 32.4 x 45.8 cm, or approximately 12.76 x 18.03 in.
What is C3 in pixels at 300 DPI?
C3 at 300 DPI is 3827 x 5409 px when rounded to the nearest whole pixel.
What aspect ratio is C3?
C3 has an aspect ratio of about 1:1.4136 based on its 324 x 458 mm physical dimensions.
Should I add bleed to a C3 design?
Envelope print workflows vary by provider and production method. Confirm bleed, flap, and safe-area requirements with the printer or envelope template before output.
References
Sources and references
ISO 269 physical dimensions. Pixel values are calculated from millimeters / 25.4 x DPI and rounded to whole pixels.
-
ISO 269:1985
Used for ISO C envelope dimensions and DL envelope references.
-
HP paper size reference
Used as a reputable printer reference for North American office, ANSI, and envelope dimensions.
-
W3C CSS Values and Units Module
Used for CSS unit definitions, absolute unit relationships, and CSS px behavior.
Last checked: 2026-05-01