Choosing the Right Envelopes: Explaining DL, C4, C5, and Window Envelopes

by Wiepa GmbH on Jul 01, 2026

Office Supplies Guide

Choosing the Right Envelopes: Explaining DIN long, C4, C5, and Window Envelopes

DIN long is the standard for business letters. C4 is suitable for unfolded DIN A4 documents. C5 fits DIN A4 documents folded once.

Envelopes are used daily in the office, yet often something is ordered quickly. This leads to incorrect formats, unsuitable window positions, or unnecessary effort in shipping.

View DIN long envelopesView window envelopes

Short Answer

For classic business letters, DIN long is usually the correct choice. For unfolded DIN A4 documents, C4 is suitable. For documents folded once, C5 is practical. Window envelopes save time if the address and window position match the letterhead.

The most important envelope formats

Format Suitable for Typical Use
DIN long DIN A4 letters folded twice Invoices, cover letters, offers
C5 DIN A4 documents folded once Documents with less folding
C4 Unfolded DIN A4 documents Contracts, folders, applications
Shipping bag More extensive documents Catalogs, brochures, document sets

DIN long: The standard for business letters

DIN long envelopes are particularly common in the office. They match classic letterheads, invoices, reminders, offers, cover letters, and mass mailings.

C4 or C5: When documents should remain pristine

C4 envelopes are useful when DIN A4 documents are to be sent unfolded. C5 is suitable if documents are only folded once and should appear more high-quality than in a DIN long envelope.

Window envelopes or no window?

Window envelopes save time if the address is already in the document and appears correctly in the window. Envelopes without windows are more flexible if address labels are used or if shipping is more individualized.

  • Window envelopes for mass mailings and invoices
  • No window for individual mail
  • Labels for changing recipients
  • Shipping bags for extensive documents

What companies should standardize

For companies, a small core assortment is worthwhile. Usually, DIN long window envelopes, DIN long plain envelopes, C4 envelopes, and suitable shipping bags are sufficient. This keeps procurement simple and mail delivery reliable.

Also relevant: Printer paper formats DIN A4, A3, A5 explained

Frequently Asked Questions

Which envelope fits a normal business letter?

For normal business letters, DIN long is the standard format.

When are C4 envelopes needed?

C4 envelopes are suitable for unfolded DIN A4 documents, contracts, folders, and important documents.

Are window envelopes useful?

Yes, if the address and window position match the document. They save time for mass mailings and invoices.

Sources and Guidance

This article serves as practical guidance for office supplies and mail shipping. Key factors are document format, folding, window position, paper quantity, and the desired impression on the recipient.

Related pages: Office Supplies, Office Supplies Service, E-Procurement and Labels in the Shop

Organize mail shipping more easily

Wiepa supports companies in Wiesbaden and Rhein Main with envelopes, shipping bags, labels, printer paper, and reliable office supplies.

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