✉️ C-series envelopes size chart
C-series envelope sizes designed to hold A-series sheets without folding or with a single fold. Centimetres are shown by default; switch units below.
C-series envelopes – all sizes
| Category | Size (cm) | Area | Common uses |
|---|---|---|---|
| C0 | 91.7 × 129.7 cm | 11,893.49 cm² | Envelopes, Cards and invitations, Mailings |
| C1 | 64.8 × 91.7 cm | 5,942.16 cm² | Envelopes, Cards and invitations, Mailings |
| C2 | 45.8 × 64.8 cm | 2,967.84 cm² | Envelopes, Cards and invitations, Mailings |
| C3 | 32.4 × 45.8 cm | 1,483.92 cm² | Envelopes, Cards and invitations, Mailings |
| C4 | 22.9 × 32.4 cm | 741.96 cm² | Envelopes, Cards and invitations, Mailings |
| C5 | 16.2 × 22.9 cm | 370.98 cm² | Envelopes, Cards and invitations, Mailings |
| C6 | 11.4 × 16.2 cm | 184.68 cm² | Envelopes, Cards and invitations, Mailings |
| C7 | 8.1 × 11.4 cm | 92.34 cm² | Envelopes, Cards and invitations, Mailings |
| C8 | 5.7 × 8.1 cm | 46.17 cm² | Envelopes, Cards and invitations, Mailings |
| C9 | 4 × 5.7 cm | 22.8 cm² | Envelopes, Cards and invitations, Mailings |
| C10 | 2.8 × 4 cm | 11.2 cm² | Envelopes, Cards and invitations, Mailings |
About C-series envelopes
C-series envelope sizes designed to hold A-series sheets without folding or with a single fold.
ISO A-series paper uses a 1:√2 aspect ratio: each size is half the area of the previous one, so A4 (210 × 297 mm) folds neatly down to A5 and enlarges to A3.
B-series paper is used for posters, books and envelopes; C-series envelopes are sized so an A4 sheet folds to fit a C5 envelope. Chinese K-sheet sizes (16K, 8K, 32K) remain common in books and notebooks.
C-series envelopes FAQ
What size is A4 paper?
A4 is 210 × 297 mm (21 × 29.7 cm, 8.27 × 11.69 in).
How many A4 sheets fit on A3?
Two: A3 is 297 × 420 mm, exactly twice the area of A4.