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Check ISO 269 standard C series envelope sizes with an exact millimeter and inch conversion chart and visual comparison guide.
Overview
Understand what the tool solves, how it works, and the boundaries of its data.
This reference lists eleven named C-series sizes. Each row shows the shorter side first, then the longer side, in millimeters and approximate inches. For example, C4 is 229 × 324 mm (about 9.0 × 12.8 in), and C5 is 162 × 229 mm (about 6.4 × 9.0 in). Rotate the dimensions for landscape orientation; the size designation does not change.
The chart is specifically for the international C series. U.S. envelope names such as No. 10 and the U.S. Letter paper system are different references. ISO 269:1985 concerned correspondence envelopes for postal purposes, but ISO records that edition as withdrawn in 2009; the chart is a dimensions lookup and does not certify a current mailing standard.
The listed millimeter dimensions are the chart values. Inch values are calculated by dividing each side by 25.4 and rounding to one decimal place. For instance, 229 mm ÷ 25.4 is about 9.016 in, shown as 9.0 in. Use the millimeter value when a project needs more precision.
C4 is nominally larger than an A4 sheet at 210 × 297 mm, which is why it is commonly compared when an A4 document must remain flat. A4 folded once has A5 dimensions, so C5 is a useful starting comparison; folded twice, it has A6 dimensions, making C6 a starting comparison. Actual fit depends on the envelope’s inside dimensions, construction, paper thickness, and clearance.
Guide
Follow the workflow and verify inputs and outputs with practical examples.
Enter a label such as C5 or a dimension such as 162 to narrow the rows. The table can also be sorted by its column headings.
Use the millimeter column for nominal dimensions; the sides are short × long. The inch column is a one-decimal approximation.
Write both the C number and dimensions, such as “C5, 162 × 229 mm,” so the reference remains clear when shared.
Use cases
See how the tool fits into real work and everyday tasks.
When preparing an unfolded A4 document, compare its 210 × 297 mm page with C4’s nominal 229 × 324 mm. Confirm the real envelope’s internal space before ordering.
A designer can record the nominal C designation and millimeter dimensions on a job brief, then verify material, flap, and clearance details with the supplier.
Compare a C-series label in a printer or document setup with the chart’s dimensions. Confirm device support and feed orientation in the equipment documentation.
Q&A
Find concise answers to common questions and confusing cases.
The chart lists C4 as 229 × 324 mm, approximately 9.0 × 12.8 inches. The inch figures are rounded to one decimal place.
No. The nominal outside dimensions are larger than A4, but usable interior space and clearance depend on the particular envelope construction.
No. C-series designations are an international size family; U.S. commercial envelope sizes use different names and measurements.
No. ISO lists ISO 269:1985 as withdrawn on April 27, 2009. This page remains a nominal dimensions reference, not a statement that the edition is current.
Notes
Review scope, result limitations, and important precautions before use.
A nominal size chart cannot confirm the usable inside dimensions of a particular envelope or whether it meets a carrier’s mailing rules.
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