C3 envelope size and dimensions
A C3 envelope measures 324 × 458 mm, which is 32.4 × 45.8 cm or 12.76 × 18.03 inches. It takes an A3 sheet flat.
Contents of this page
C3 envelope, portrait
324 × 458mm
- Centimetres
- 32.4 × 45.8 cm
- Inches
- 12.76 × 18.03 in
- Pixels at 300 dpi
- 3827 × 5409 px
- Points (pt)
- 918 × 1298 pt
- Area
- 0.1484 m²
- Weight at 80 gsm
- 11.9 g
C3 is the envelope for anything in A3 that must not be folded: drawings, certificates, calendars, photos and presentations. It is twice the size of a C4 envelope and therefore too big to go as any kind of letter. That is the main thing to know before you buy a box of them.
C3 in every unit
| Unit | Width × height |
|---|---|
| Millimetres | 324 × 458 mm |
| Centimetres | 32.4 × 45.8 cm |
| Metres | 0.324 × 0.458 m |
| Inches | 12.76 × 18.03 in |
| DTP points (1/72 in) | 918 × 1298 pt |
| Area | 1483.9 cm², or 0.1484 m² |
| Diagonal | 561 mm |
| Aspect ratio | 1 : 1.414 |
What fits in a C3 envelope
| Contents | Size | Fits? |
|---|---|---|
| A3 flat | 297 × 420 mm | yes, with 13.5 mm at the sides and 19 mm at the top and bottom |
| A3 wall calendar with wire binding | about 297 × 420 mm, a few mm thick | yes, ideally board-backed |
| C4 envelope with A4 contents | 229 × 324 mm | yes |
| US Tabloid | 279.4 × 431.8 mm | yes, just |
| B3 poster | 353 × 500 mm | no |
Why C3 cannot go as a letter
Royal Mail's Large Letter stops at 353 × 250 mm, and the German Maxibrief has the same limit. A C3 envelope is larger on both sides and has to go as a parcel. With Royal Mail it is even 8 mm too long for a Small Parcel, which allows up to 45 × 35 × 16 cm, so it falls into the next parcel size. Check the current limits with your carrier before you have a large batch printed.
If it has to be a letter after all, there are two ways round it:
- Fold the A3 sheet once and send it in a C4 envelope as a Large Letter. A bone folder gives a clean crease.
- Roll it and send it in a postal tube. That is a parcel too, but it protects the sheet better.
Weight
An A3 sheet of 80 gsm paper weighs about 10 g. A C3 envelope in sturdy paper adds roughly 25 to 40 g depending on the make, and considerably more with a board back. A letter scale takes the guesswork out of postage.
Frequently asked questions
How big is a C3 envelope?
324 × 458 mm, which is 32.4 × 45.8 cm.
Does A3 fit in a C3 envelope?
Yes, flat. It leaves 13.5 mm at the sides and 19 mm at the top and bottom.
Can I post a C3 envelope as a Large Letter?
No. It is larger than the Large Letter limit of 353 × 250 mm and goes as a parcel.
How do I post A3 as a letter?
Fold it once and send it in a C4 envelope as a Large Letter.
Which is bigger, C3 or B3?
B3 at 353 × 500 mm. C3 sits between A3 and B3.