Reference library

C1 Envelope Paper Size

C1 measures 648 x 917 mm, 64.8 x 91.7 cm, or 25.51 x 36.1 in. See pixel dimensions by DPI, aspect ratio, bleed setup, comparisons, and related tools.

Last checked: 2026-05-01

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At a glance

C1 is 648 x 917 mm, 64.8 x 91.7 cm, or 25.51 x 36.1 in. At 300 DPI, C1 is 7654 x 10831 px.

Last checked: 2026-05-01 Source: ISO 269:1985 Found a spec change? Send correction.

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.

Methodology Editorial policy

Quick answer

Copy-ready answer

C1 is 648 x 917 mm, 64.8 x 91.7 cm, or 25.51 x 36.1 in. At 300 DPI, C1 is 7654 x 10831 px.

648 x 917 mm

Dimensions and specs

Millimeters	648 x 917 mm
Centimeters	64.8 x 91.7 cm
Inches	25.51 x 36.1 in
300 DPI pixels	7654 x 10831 px
Aspect ratio	1:1.4151
Standard family	ISO C Envelope Series

Pixels

Pixel dimensions by DPI

DPI / PPI	Width	Height	Use
72 DPI	1837 px	2599 px	Screen or draft reference density
96 DPI	2449 px	3466 px	Screen or draft reference density
150 DPI	3827 px	5415 px	Screen or draft reference density
300 DPI	7654 px	10831 px	Common high-quality print setup
600 DPI	15307 px	21661 px	High-resolution archival or print workflow

Formula

How to calculate this size

Pixel formulapixels = millimeters / 25.4 x PPI

648 mm x 300 PPI = 7,654 px wide.

Trim result7,654 x 10,831 px

Use this when the artwork stops at the finished edge.

Bleed result7,654 x 10,831 px

Add 0 mm per side before calculating pixels when artwork reaches the edge.

Common mistakes

Avoid these c1 envelope paper size problems

Mixing screen pixels with print quality

A paper size needs a PPI target before pixels mean anything for print.

Forgetting orientation

Portrait and landscape use the same dimensions, but width and height swap in the export.

Adding bleed to a paper reference

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 C1 Envelope Paper Size

Open a curated comparison or send both sizes into the compare tool with a fragment URL.

compare tool C1 vs C0

C1 Envelope Paper Size: 648 x 917 mm
C0: 917 x 1297 mm

50% smaller than C0 Envelope Paper Size. nearly identical aspect ratio compare tool C1 vs C2

C1 Envelope Paper Size: 648 x 917 mm
C2: 458 x 648 mm

100.2% larger than C2 Envelope Paper Size. nearly identical aspect ratio compare tool C1 vs A4

C1 Envelope Paper Size: 648 x 917 mm
A4: 210 x 297 mm

852.7% larger than A4 Paper Size in Pixels, Millimeters, Centimeters and Inches. nearly identical aspect ratio compare tool C1 vs US Letter

C1 Envelope Paper Size: 648 x 917 mm
US Letter: 215.9 x 279.4 mm

885.1% larger than US Letter Paper Size. 0.0661 decimal ratio difference

C1 belongs to the ISO C Envelope Series family. Use this reference for print setup, document layout, template sizing, pixel conversion, and comparisons with nearby paper sizes. Pixel dimensions are calculated from the physical size and selected DPI.

Workflow

Use C1 Envelope Paper Size in a finished file

Confirm the physical size

Copy the millimeter, centimeter, or inch dimensions for the selected paper standard.

Choose PPI

Use 300 PPI for most sharp print exports, or match the printer requirement.

Calculate pixels

Multiply inches by PPI, then add bleed only when artwork reaches the trimmed edge.

Related pages and tools

same series C0 paper size same series C2 paper size common alternative A4 paper size common alternative US Letter paper size comparison C1 vs C0 comparison C1 vs C2 tool DPI calculator tool Print bleed calculator tool Compare sizes tool

Same branch

Nearby pages

A4 Paper Size in Pixels, Millimeters, Centimeters and Inches A5 Paper Size Legal Paper Size US Letter Paper Size A0 Paper Size A1 Paper Size A10 Paper Size A2 Paper Size

FAQ

Common questions

What is the exact C1 size?

C1 measures 648 x 917 mm, 64.8 x 91.7 cm, or approximately 25.51 x 36.1 in.

What is C1 in pixels at 300 DPI?

C1 at 300 DPI is 7654 x 10831 px when rounded to the nearest whole pixel.

What aspect ratio is C1?

C1 has an aspect ratio of about 1:1.4151 based on its 648 x 917 mm physical dimensions.

Should I add bleed to a C1 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