C4 vs C5
C4 is 229 × 324 mm; C5 is 162 × 229 mm. C4 holds an A4 sheet flat; C5 holds A4 folded once or A5 flat. C4 is exactly twice C5, and the two share the 1:√2 shape of the C series.
| C4 | C5 | Difference | |
|---|---|---|---|
| Width | 229 mm | 162 mm | +67 mm |
| Height | 324 mm | 229 mm | +95 mm |
| Inches | 9.02 × 12.76 in | 6.38 × 9.02 in | |
| Pixels @ 300 dpi | 2,705 × 3,827 | 1,913 × 2,705 | |
| Area | 742 cm² | 371 cm² | 200% |
| Aspect ratio | 1:√2 | 1:√2 | |
| Scale to fit | C4 → C5: 71% | C5 → C4: 141% |
Choose C4 when
Use C4 for documents that must arrive unfolded: certificates, contracts, photographs, brochures and reports of more than about 20 pages. It is the standard large envelope for A4 and the size document wallets are made in.
Choose C5 when
Use C5 for A4 letters folded once, A5 booklets, greeting cards and packs of a few sheets. It is cheaper to buy, cheaper to post and fits through most letterboxes flat.
Which should you use?
Fold once if you can and use C5; send flat in C4 only when folding would damage or devalue the contents. Most postal services charge C4 as a large letter, so the choice affects cost as well as presentation.
Insert clearance is generous in both. A4 in C4 has 19 mm spare width and 27 mm spare height; A4 folded once in C5 has 7 to 9 mm each way. For packs thicker than about 5 mm choose a gusseted C4 rather than a standard wallet.
Window positions differ between the two sizes, so a letter designed for a C5 window will not show its address correctly through a C4 window. Check the window template before a mailing.
Questions about this comparison
What size is a C4 envelope?
C4 is 229 × 324 mm (9.02 × 12.76 in). It holds an A4 sheet (210 × 297 mm) flat with 19 mm of spare width and 27 mm of spare height.
Does A4 fit in a C5 envelope?
Only folded once, to 210 × 148 mm. C5 is 162 × 229 mm, so a flat A4 sheet is 48 mm too wide and 68 mm too tall.
Is C4 twice the size of C5?
Yes. C4 (229 × 324 mm) is two C5 envelopes (162 × 229 mm) side by side, exactly as A4 is two A5 sheets.
Scale one onto the other
The exact percentage for the print dialog, either direction.
Measure it, name it
Not sure which one you have? Type its width and height.