Envelope size guide

Format Dimension (mm) Suitable for
DL 110 x 220 DL flyers (99 x 210 mm), A5 folded once, A4 folded into thirds
DLX 120 x 235 Mail out, fits more documents than a DL size
C6 114 x 162 A6, A5 folded one, A4 folded in half twice
C5 162 x 229 A5, A4 folded once
C4 229 x 324 A4 unfolded, A3 folded once
C3 324 x 458 A3 unfolded


Flap styles

Pocket Wallet
An envelope that opens on the short edge. An envelope that opens on the long edge.


  • Lick and Stick: Requires moisture to close.
  • Peel and Seal: Remove plastic strip, fold over and press to close.
  • Self Seal: Pre-gummed bottom flap for ease of closure, no moisture required, no plastic strip

Internal lining

  • Non-Secretive: Plain paper, the envelope could be see-through.
  • Secretive: The paper has a printed internal pattern that prevents it from being see-through.


  • Plain face: No windows.
  • Window face: Has a clear window on the front. Recommended for mail merge.

Due to increased automation in mailing processing, Australia Post applies limits on the size and shape of articles that qualify for the standard postal size. Australia Post provides a free letter gauge that indicates if articles fall into the standard category. Non standard envelopes will incur additional charges. For rules and regulations regarding postage please refer to: www.austpost.com.au