C5 Envelope
C-Series Envelopes (ISO 269) · 7 specs
Direct Answer
The C5 envelope is an ISO 269 standard postal envelope measuring 162 × 229 mm (6.38 × 9.02 inches). Designed to enclose an A4 sheet folded once in half (V-fold) or an unfolded flat A5 document (148 × 210 mm), it is standard for greeting cards, invitations, company invoices, and small paperback book shipments.
Source: ISO 269:1985 (DIN 678) · Last reviewed Aug 28, 2026
Specs
| Width × Height (Metric) | 162 × 229 mm |
| Width × Height (Imperial) | 6.38 × 9.02 in |
| Geometric Mean Origin | Geometric mean of A5 (148×210 mm) and B5 (176×250 mm) |
| Target Paper Pairing | A4 folded in half (148 × 210 mm) or flat unfolded A5 stationery |
| Paper Insertion Clearance | +14 mm width / +19 mm height clearance |
| Window Options | Standard left-hand or right-hand clear address window (45 × 90 mm) |
| Primary Applications | Greeting cards, event invitations, invoices, corporate brochures |
Single-Fold A4 Efficiency
Folding an A4 sheet in half across its length turns it into an exact A5 footprint (148 × 210 mm). Inserting this into a C5 envelope (162 × 229 mm) cuts required envelope surface area in half compared to C4, substantially reducing envelope paper consumption while maintaining lower letter-class postage rates.