C4: the envelope for unfolded A4
An A4 sheet (210 × 297 mm) fits unfolded into a C4 envelope (229 × 324 mm). That is the standard choice for:
- certificates and diplomas,
- contracts and official documents,
- application folders,
- anything that must not have a crease.
Folded into thirds, A4 fits the standard DIN long envelope — perfectly fine for ordinary letters and cheaper to post.
Cardboard mailers: when it really matters
For documents that must not be bent under any circumstances there are cardboard mailers with stiff board or a "do not bend" marking. They weigh more but protect reliably. Keep in mind: the extra weight can push the letter into the next postage tier.
Which postage applies?
A C4 envelope with a few sheets is usually a Großbrief; with more contents or heavy board it becomes a Maxibrief. Size and weight decide:
- Großbrief: up to 500 g, max 2 cm thick,
- Maxibrief: up to 1,000 g, max 5 cm thick.
The postage calculator works out the current price for your letter. The differences are explained in Großbrief or Maxibrief.
Don't forget the addressing
C4 envelopes come with and without a window. Without a window you label the envelope as usual — recipient bottom right, sender top left or on the back. Details are in the guide Addressing an envelope correctly. Even easier: in the letter editor your document is printed and sent in the right envelope — no folding or franking questions at all.