Envelopes are the unsung heroes of the paper world. The wrong envelope can crumple your letter or make your invitation look amateur. Understanding the relationship between paper sizes and envelope sizes saves time and money.
The ISO C Series: Designed for A Series
ISO 269 defines the C series specifically to fit A series paper. A Cn envelope holds an An sheet unfolded, or an An+1 folded once, or an An+2 folded twice:
- C4 — 229 × 324 mm — holds A4 flat
- C5 — 162 × 229 mm — holds A4 folded once, A5 flat
- C6 — 114 × 162 mm — holds A4 folded twice, A6 flat
- C7 — 81 × 114 mm — small cards
DL: The Business Envelope
DL ("Dimension Lengthwise") is the standard business envelope in Europe: 110 × 220 mm, holding an A4 sheet folded into three panels.
US Envelopes: The Numbering System
- #10 — 4.125 × 9.5 in — standard US business envelope
- #9 — 3.875 × 8.875 in — personal correspondence
- #6¾ — 3.625 × 6.5 in — greeting cards
- #11 — 4.5 × 10.375 in — larger mailings
Choosing the Right Envelope
- Identify your contents
- Decide on folding style
- Add 3–5 mm margin on each side
- Check postal service requirements