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Check ISO 269 standard C series envelope sizes with an exact millimeter and inch conversion chart and visual comparison guide.
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When you need to choose an envelope for an A4 document but aren't sure whether to use C4 or C5, this tool provides the exact answer. Based on the ISO 269 international standard, this tool offers complete dimension data for C series paper (envelopes). It outputs a precise size chart from C0 to C10, including both millimeters (width × height) and inches (width × height), along with an intuitive visual comparison chart to help you quickly understand the differences in specifications. The C series is specifically designed as the "standard envelope size" for enclosing corresponding A series paper.
Q: What is the standard size of a C4 envelope?
The standard size of a C4 envelope is 229 mm × 324 mm (9.0 inches × 12.8 inches).
Q: How are C series sizes calculated, and why do they perfectly fit A series paper?
A C series size is the geometric mean of the corresponding A series and B series sizes. The formula is Cn = √(An × Bn). This mathematical relationship ensures that the internal dimensions of a C series envelope are slightly larger than the corresponding A series paper (e.g., C4 is slightly larger than A4), leaving the necessary clearance to insert the A4 paper into the C4 envelope for a perfect fit.
The dimension data provided by this tool are ISO standard values, suitable for standard envelope design and procurement. The size comparison chart on the page is primarily for visual reference, and its proportions may not be perfectly exact; please rely on the values in the table for specific dimensions. All size annotations follow the international convention of "Width × Height". This tool does not involve file uploading or batch processing features.
In printing and office supply procurement, accurately matching the envelope to the insert size is crucial. The correspondence between C series envelopes and A series paper is the core of the design: an unfolded A4 sheet fits into a C4 envelope, an A4 sheet folded in half (which is A5 size) fits into a C5 envelope, and so on. A typical application example: when printing an A4-sized invitation, you should choose a C4 envelope for mailing to ensure the document remains flat and is easy to insert. Understanding this one-to-one "A paper into C envelope" relationship can greatly improve the professionalism and efficiency of your document packaging.
