DL envelope size and what fits inside

What a DL envelope is for

DL is a long, narrow envelope sized so that a sheet of A4 folded in three slides in with a little room to spare. Because almost every business letter, invoice and statement in the UK and Europe is printed on A4 and folded that way, DL has become the standard office envelope across the UK and Europe.

DL envelopes come plain or with a window. The window sits on the left, at the height where the recipient's address ends up once the letter is folded, so the address is printed on the letter and shows through. In Germany the DIN 5008 standard fixes where the address field goes on the page, which means letters and windows line up reliably. UK windows are in the same general area but vary slightly between makers, so fold one finished letter and test it before you print a batch. With a plain DL, the address goes on the envelope itself.

What fits inside a DL envelope

A4 folded in three gives three panels of 99 × 210 mm, and two or three sheets folded together still go in comfortably. Anything already a third of A4 goes in flat, which is why compliment slips, DL leaflets and DL invitation cards are cut to that size. A compliment slip clipped to a brochure or a cheque is the classic example. An A6 postcard fits too, but it slides about, so a C6 envelope is the neater choice for it.

If the fit is tight, use C6/5, sometimes sold as DL+. It's slightly larger each way and takes folded A4 with room to spare, which helps when you're sending several sheets, when your folds aren't quite even, or when you're folding US Letter, which comes out a little longer than folded A4 and only just fits a DL. For A4 folded once, a C5 envelope is the right size, and the US counterpart of DL is the #10 envelope.

Printing the address on a DL envelope

Most home printers take paper up to US Letter width, and a DL envelope fed short edge first is comfortably inside that. Put it in the rear or manual feed with the flap closed; the envelope icon on the tray, or the printer's manual, shows which side faces up and whether the flap leads or trails. Choose "Envelope DL" as the paper size in the print dialogue so the printer doesn't expect an A4 page, and on a laser printer use the envelope setting so the flap doesn't crease. Printing once on plain paper and holding the sheet against an envelope is a cheap way to check the position.

The template behind the button on this page handles a single envelope, and for a whole mailing list you can print addresses from an Excel or CSV file with a free account, one envelope per address. If your printer won't take envelopes at all, address labels on an A4 sheet do the same job, because you print the sheet like a normal page and stick one label on each envelope. The guide to printing envelopes covers feed problems in more detail.

Which postage format a DL envelope counts as

Royal Mail sorts post into Letter, Large Letter and parcels by size, thickness and weight, and a DL envelope sits inside the Letter dimensions. A normal letter in a DL therefore goes at the Letter price; it only becomes a Large Letter if it gets too thick or too heavy, say with a chunky brochure inside. Deutsche Post and most other European operators also treat DL as a standard letter, so the weight and thickness decide the price rather than the envelope.

USPS counts a DL envelope as a letter, just like a #10, as long as it stays thin and light enough. If the contents make it thicker or heavier than the letter limits allow, it's charged as a large envelope (a "flat") instead, which costs more, in the same way a chunky DL becomes a Large Letter in the UK. Stiffness matters too: a DL with something rigid or lumpy inside, such as a key or a thick card, may not go through the sorting machines and can cost extra as a non-machinable letter. As a rough guide, an A4 sheet of ordinary 80 g/m² paper weighs about 5 g and the envelope about the same, so a two-page letter comes to around 15 g. Weigh anything heavier before you choose your stamps.