What envelope size is best for A4 paper?

DL envelopes (110 × 220 mm) fit A4 paper folded in thirds. C5 envelopes (162 × 229 mm) fit A4 paper folded in half.

How do you fold A4 paper into three equal parts?

Fold the bottom edge up by 99 mm, then fold the top edge down by 99 mm. This leaves three equal 99 × 210 mm panels.

What is DIN 5008 standard for letter folding?

DIN 5008 is the German national standard for business letter formatting and folding, specifying exact margins so address fields align with DL window envelopes.

How do I fold A4 paper for a C6 envelope?

Fold the A4 sheet in half horizontally, then fold it in half vertically (quarter-fold).

Interactive Paper Folding Tutor

Updated: September 20, 2026

ISO 269 International Mailing Standard

How to Fold A4 Paper for DL & C5 Envelopes

A4 paper (210 × 297 mm) is the standard paper size used throughout Europe, Asia, Latin America, and Africa. ISO 269 & DIN 5008 standards specify exact folding techniques for DL and C5 commercial envelopes.

International Business Mail Standards

Ideal for international invoices, cross-border business correspondence, European administrative forms, and DIN 5008 window envelope mailings.

International ISO Envelope Sizes

ISO DL (110 × 220 mm) • ISO C5 (162 × 229 mm) • ISO C6 (114 × 162 mm)

Step-by-Step A4 Folding Instructions

Position A4 Sheet: Place A4 sheet (210 × 297 mm) portrait face up on a flat surface.
Fold Bottom 99mm Up: Fold bottom panel upward by exactly 99 mm (1/3 of the 297 mm length).
Fold Top 99mm Down: Fold top panel downward over the bottom section to form a 99 × 210 mm rectangle.
Insert into DL Envelope: Slide folded A4 letter into a DL envelope (110 × 220 mm) leaving 11mm side clearance.

Envelope TypeDimensionsBest Fold

#10 Business4.125 × 9.5 inTri-Fold

DL Envelope110 × 220 mmA4 Tri-Fold

#10 Window4.125 × 9.5 inZ-Fold

C5 / 6×9 in162 × 229 mmHalf-Fold

A2 / C6 Card4.375 × 5.75 inQuarter-Fold

ISO 269 International Mailing Standard Technical Diagram

A4 Stationery Best Practices

A4 paper is longer and narrower than US Letter; ensure you use DL envelopes rather than US #10.
For DIN 5008 window envelopes, position the recipient address block in the top-left panel area.
Use a single half-fold for C5 envelopes when sending certificates or legal contracts.

A4 Mailing Mistakes

Trying to fit A4 tri-folded paper into US #10 envelopes (A4 is 297mm long vs 279.4mm US Letter).
Folding A4 unevenly resulting in address blocks missing envelope windows.
Creasing heavy 100+ gsm A4 paper without scoring first.

Envelope & Paper Size Compatibility Matrix

Match your sheet dimensions to standard commercial envelopes to prevent postage delays and bulky mailings.

Envelope TypeDimensionsBest Fold

#10 Business4.125 × 9.5 inTri-Fold

DL Envelope110 × 220 mmA4 Tri-Fold

#10 Window4.125 × 9.5 inZ-Fold

C5 / 6×9 in162 × 229 mmHalf-Fold

A2 / C6 Card4.375 × 5.75 inQuarter-Fold

Explore Related Folding Guides

How to Fold a Letter for an Envelope How to Fold a Letter Into an Envelope How to Fold Paper Into Thirds (Tri-Fold Guide) How to Fold A4 Paper for DL & C5 Envelopes Interactive Z-Fold Accordion Guide Origami Self-Mailing Letter Fold

Frequently Asked Questions About Folding Letters

Answers to common stationery, business mailing, and postal envelope folding questions.

A4 measures 210 × 297 mm (8.27 × 11.69 in), making it narrower and taller than US Letter, which measures 215.9 × 279.4 mm (8.5 × 11 in).