Window envelopes and the address field

A window envelope only works when three things agree: the position of the recipient address, the fold of the sheet, and the position of the window. In Germany all three are standardised — and the tolerances are narrow.

The formats

Format	Size	Use
DIN lang (DL)	220 × 110 mm	the standard for business mail; takes one A4 sheet folded in thirds
C6	114 × 162 mm	half an A4 sheet, folded once
C6/C5	110 × 229 mm	one A4 sheet, folded once
C4	229 × 324 mm	one A4 sheet, unfolded, for bulky mailings

For business letters DIN lang is the norm. The name is somewhat misleading: it is not itself a DIN standard but the established German name for the 220 × 110 mm format.

Where the window sits

Window positions are specified in DIN 680. For DIN lang, C6 and C6/C5, the arrangement common in Germany is:

Window size: 90 × 45 mm
Distance from the left edge: 20 mm
Distance from the bottom edge: 15 mm

C4 envelopes often use a larger window, frequently 90 × 55 mm.

Why the address field is 85 mm wide, not 90 mm. The window is 90 mm wide, the DIN 5008 address field 85 mm. The 5 mm difference is deliberate tolerance. A folded sheet is never inserted to the millimetre; without the margin, a small shift would clip the address. Widening the field removes the safety margin.

Folding to match the envelope

Envelope	Fold	Fold marks (Form B)
DIN lang (DL)	twice, into thirds (Z-fold)	105 mm and 210 mm
C6	once, in the middle	148.5 mm
C6/C5	once, in the middle	148.5 mm
C4	none	none

For the Z-fold, the bottom third is folded backwards first and the top third forwards. The recipient address stays on the outside and faces the window. Folding both creases in the same direction — a wrap fold — is more robust but turns the back of the top third outwards, which is why the Z-fold is usual for window mail.

Test it with real paper

No calculation replaces one test with an actual sheet:

Print the letterhead on A4 at actual size — no page scaling.
Fold it the way it will be folded later.
Insert it into the intended envelope and check from outside: is the whole address visible in the window? Is there clearance on all sides?
Repeat with the heaviest paper you use. 100 g/m² folds differently from 80 g/m².

This test takes a minute and catches errors that are invisible on screen — a letterhead that is too tall, or an address shifted by a few millimetres.

The three terms, distinguished

Window (Sichtfenster) — the cut-out in the envelope, specified by DIN 680.
Address window (Adressfenster) — sometimes used for the same cut-out, sometimes for the area on the letter that is meant to appear in it.
Address field (Anschriftfeld) — the area on the letter itself, 85 × 45 mm, defined by DIN 5008.

Only the sender's return address belongs on the envelope itself, and usually it is pre-printed. The recipient address goes on the letter — that is what the window is for.

Common questions

How big is the window in a DIN lang envelope?

Under DIN 680 the window in a DIN lang envelope is 90 mm wide and 45 mm high, positioned 20 mm from the left edge and 15 mm from the bottom edge.

Which envelope fits a folded A4 sheet?

For an A4 sheet folded in thirds, DIN lang (220 × 110 mm) is the standard format. A sheet folded once fits C6/C5; an unfolded sheet fits C4.

Why is the address field narrower than the window?

The window is 90 mm wide and the DIN 5008 address field is 85 mm. The 5 mm difference provides tolerance so the address stays fully visible even when the sheet is inserted slightly off-centre.

How many times is a letter folded for a DIN lang envelope?

Twice, into thirds. The DIN 5008 Form B fold marks for this fold sit at 105 mm and 210 mm from the top edge of an A4 sheet.

Create your letterhead in the browser

The TwiceDocs studio applies the measurements described here automatically: address field, fold marks, 300 DPI PDF export and print-shop bleed. Free, no sign-up, and your data never leaves your browser.

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