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Envelope reference · ISO C family

C5 envelope size

A versatile envelope that holds A5 flat or A4 folded once, making it common for letters, statements, invitations, and short document packs.

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C5162 × 229 mm
229 mm landscape162 mm
Millimeters162 × 229
Inches6.38 × 9.02
300 DPI1913 × 2705 px
Best-fit insertA5 at 148 × 210 mm flat

Direct answer

C5 dimensions and paper fit

In landscape orientation, C5 measures 162 × 229 mm, or 6.38 × 9.02 inches. A5 at 148 × 210 mm flat, or A4 folded once to A5.

UnitWidthHeight
Millimeters162 mm229 mm
Centimeters16.2 cm22.9 cm
Inches6.38 in9.02 in
Pixels at 300 DPI1913 px2705 px

Insert & folding

What fits inside C5?

A5 at 148 × 210 mm flat, or A4 folded once to A5. Fold A4 once across its long dimension to create an A5-sized insert.

Comparison

How C5 differs from nearby envelopes

C5 is 14 mm wider and 19 mm taller than A5. It is larger than a 6 × 9 inch envelope and smaller than C4.

Works well for

Common C5 uses

  • A4 letters folded once
  • A5 invitations
  • Statements
  • Small brochures

Check before using

Where it can go wrong

  • Unfolded A4
  • 6 × 9 inch print templates
  • Mailing without checking thickness limits

Postal note

Dimensions do not determine postage by themselves.

Check the carrier’s current maximum thickness and weight. A rigid or bulky C5 mailer may be priced differently from a flexible letter.

Historical measurement source

Based on the C-series envelope convention.

The official ISO page identifies ISO 269:1985 as withdrawn. Paper Size Lab cites it as the historical designation source, not as a current postal requirement.

View ISO 269:1985 status

Questions people ask

C5 envelope FAQ

What size is a C5 envelope?

C5 measures 162 × 229 mm, or 6.38 × 9.02 inches.

What paper fits in a C5 envelope?

A5 at 148 × 210 mm flat, or A4 folded once to A5.

How should paper be folded for a C5 envelope?

Fold A4 once across its long dimension to create an A5-sized insert.

Does a C5 envelope qualify for standard postage?

Check the carrier’s current maximum thickness and weight. A rigid or bulky C5 mailer may be priced differently from a flexible letter.