Flat or one fold
A5 is 148 × 210 mm. C5 provides a nominal 14 mm difference in width and 19 mm in height before construction and tolerance are considered. Folding A5 once produces an A6-sized insert for C6.
Paper & card guide
Envelope for A5 paper
C5 is the familiar envelope for A5 paper flat. C6 is the familiar next step when A5 is folded once to A6.
Nominal size reference
Compare the recorded formats
Every table uses nominal exterior width × height. International sizes lead with millimetres; US sizes lead with conventional fractional inches.
| Format | Native size (width × height) | Converted size (width × height) | Source checked | Context |
|---|---|---|---|---|
| C5International | 162 × 229 mm | 6.378 × 9.016 in | Envelope Manufacturers Association ↗27 August 2026 | A5 paper flat |
| C6International | 114 × 162 mm | 4.488 × 6.378 in | Envelope Manufacturers Association ↗27 August 2026 | A6 paper flat |
Choose C5 for presentation
Keeping A5 flat avoids a crease and is usually preferable for certificates, photographs, finished artwork or inserts intended to be displayed. Choose C6 when a fold is acceptable and compactness matters.
Allow for the physical piece
Nominal envelope dimensions describe the exterior format, not guaranteed usable internal space. Seams, lining, stock thickness, multiple pieces and manufacturing tolerances reduce practical room; sample before a bulk order or print run.