The DL format is 99 × 210 mm, meaning one third of an A4 sheet. That's not a coincidence, it's math: fold an A4 sheet into three equal parts and you get exactly DL. And that's precisely why this format fits so well into a standard office C6/5 envelope (for the DL format) - because the whole envelope was designed around this specific folded sheet, not the other way round.
Where do these formats even come from
The A4 format is 210 × 297 mm and is the mother of most of the other dimensions you work with every day. The entire A series is based on one rule: fold a sheet in half along the longer side, and you get the next format in the same series, keeping the same proportions. A4 folded in half gives you A5, i.e. 148 × 210 mm. A5 folded in half would give you A6. That's why an A5 flyer fits so nicely into an envelope designed for A4 folded once, and an A2 poster splits effortlessly into two A3 sheets.
DL lives a bit apart from this series, because it wasn't created by dividing A4 in half, but into three. And it's precisely this unusual division that made DL the favourite of everyone sending something by post or inserting a flyer into a company envelope. Try fitting an A5 into a regular long office envelope - it'll fit, but it'll flap around and curl at the corners. DL slides in perfectly, because the envelope was designed for it.
DL, A5 or A4 - how to choose in practice
The choice depends mainly on where the flyer is meant to end up after printing, not on what happens to look best in the design. There are three typical scenarios, and each one dictates a different dimension.
The flyer is meant to go into an envelope
DL (99 × 210 mm) is almost the automatic choice here, since it's the only one of the three formats specifically designed for mailing. It fits a standard DL envelope without folding, which matters for mailings, sales offers sent by post, or flyers enclosed with invoices. If you're designing something meant to land in a client's mailbox next to an electricity bill, think DL.
The flyer is meant to stand in a display stand on a counter
This is where things get complicated, because display stands (the plastic ones with compartments, standing by the till or at reception) are most often designed specifically for DL. It's a kind of domino effect: since DL dominates office mailings, stand manufacturers went the same way, and most standard counter holders have a compartment width matched to 99 mm. Before you order a print run in A5 thinking it
will fit everywhere, physically check the stand the flyer is meant to go in. An A5 simply won't fit into a narrow DL compartment, and if you force it, the flyer will bend and fall out at every touch.
The flyer is meant to be handed out directly or read as a standalone document
A5 (148 × 210 mm) works best here, as it's a compromise between readability and handiness. It fits more content than DL, still holds comfortably in the hand, and doesn't need folding. If the flyer has more text, a price list, a location map or several product photos, DL starts feeling cramped and the designer begins fighting over every millimetre. A5 gives some breathing room.
A4 (210 × 297 mm), in turn, is the choice when the flyer is meant to function as an informational poster, a menu, a price list to be pinned on a board, or material the client takes along to read comfortably at their desk. You don't fit an A4 into any office envelope without folding, so if the design must go into an envelope anyway, A4 forces an extra production step, namely folding.
Folding A4 into a DL envelope - what happens to the format
A4 folded into three (the so-called C-fold, or simply folding into three equal parts) gives a dimension roughly close to DL, and that's exactly why it fits so well into the same envelope. This is a common choice for sales offers, where there's more content than fits on DL, but the company still wants to send it by post in a standard office envelope.
The problem is that folding changes the rules of the game in the graphic design. Every panel of a folded flyer has its own logic: elements meant to be readable after folding (such as a heading or a call to action) need to land on the panel visible on the outside, not the inside. The fold line (i.e. the crease) requires a safety margin, because text or a logo placed exactly on the fold line simply cracks or wears away with repeated opening. In practice, this means keeping important elements a few millimetres away from the fold line at every crease, not right on it.
Folding isn't a detail, it's a different design: If you're planning an A4 folded into DL, design it from the start with the panel division in mind, and consult the layout before sending it to print. Fixing the layout after a finished print run has been folded isn't a correction anymore, it's a complaint.
Net format, gross format, and why it matters for every one of these dimensions
The net format is the flyer's dimension after trimming, the one you quote to the client and the one they see in their hands. The gross format is the dimension of the file you actually send to print, larger by the bleed. The standard bleed for this type of job is 3 mm on each side, because the cutting machine works on a stack of sheets, and even with a perfectly set guillotine, micro-shifts of a fraction of a millimetre can occur between the first and last sheet in the stack.
Let's take A5 as a numerical example. The net format is 148 × 210 mm. You add 3 mm of bleed on each side, so you add 6 mm in total to both width and height (3 mm on the left plus 3 mm on the right, and likewise top and bottom). The gross format, meaning the dimension of the file you actually send, comes out to 154 × 216 mm. Backgrounds, photos, coloured areas must reach all the way to this larger edge, otherwise after trimming you'll see a thin white strip where a solid background was supposed to be.
With DL the mechanism is identical: net 99 × 210 mm, gross 105 × 216 mm. The difference sounds harmless until you forget to account for it, and then you get a call from a client asking why there's a white line on the edge of their flyer.
The safety margin is a different matter from the bleed
The bleed accounts for what happens outside the cutting line, the safety margin accounts for what happens just inside it. These are two different concepts, and confusing them is one of the most common mistakes we see in files from clients. The safety margin from the cutting line is a minimum of 3 mm, and for multi-page jobs, catalogues or brochures 5 mm or more is recommended, since there's also the added risk related to binding and the spine.
In practice, this means that all important text, logos, phone numbers should sit at least 3 mm inward from the net edge, not from the gross edge. If you place a heading literally right on the cutting line, all it takes is the blade shifting half a millimetre in the wrong direction and the text gets cut through the middle of a letter. With DL, which is narrow anyway (99 mm wide), this margin becomes especially important, since there's less room for error than with A4.
The bleed extends outward from the cutting line and protects against a white stripe. The safety margin extends inward from that same line and protects against cutting off text. These are two different zones, measured in two different directions from the same net edge.
Paper, finishes and the choice of format
A format rarely exists independently of the paper it's meant to be printed on, and that's also worth thinking through before sending the file. DL and A5 flyers for display stands are usually printed on gloss or matte coated paper in a weight range of 115-350 gsm, depending on whether the flyer is meant to be light and cheap for mass distribution, or more premium and rigid. Thinner coated stock, closer to the lower end of this range, works well for large runs handed out in the street, since it's cheaper to transport and lighter in hand. Thicker stock, closer to the upper end, holds its shape better in a display stand and doesn't bend just from being picked up.
An A4 folded for an envelope is a different story, because folding rigid paper heavier than 170 gsm starts causing problems: it cracks at the fold if not pre-scored, and doesn't fold evenly. Uncoated offset paper in the 80-140 gsm range works better for jobs meant mainly to be read as text, without heavy colour saturation across the whole surface.
The most common mistakes when choosing a format
The first and most common one: someone designs a flyer in A5 because
it looks nicer and fits more content, orders the print run, and then it turns out they have DL stands bought a year earlier. The whole run looks in them like an umbrella crammed into too small a case. Checking the stand takes literally a minute, and it saves having to redo the entire design.
The second mistake is designing an A4 for an envelope without accounting for folding. The designer creates one consistent image across the whole surface, without thinking that once folded into three, that image will be cut into panels that don't necessarily connect logically with each other once opened. The result: a logo cut exactly through the middle at the fold, a heading that ends up on an inner panel instead of an outer one.
The third, more prepress-related one: confusing the net format with the gross format when sending a file to print. Someone prepares a file at exactly 148 × 210 mm with no bleed, because
it's that format anyway, and then is surprised by a white border on the finished run. I once saw a file myself where the background sat exactly on the net format boundary, without a single millimetre to spare, and the client was convinced it was the printer's fault, not the file's.
Format isn't a cosmetic detail: A poorly chosen format means either a flyer that doesn't fit into the envelope or stand, or a costly reprint of the whole run after someone notices the problem only at pickup. Checking the flyer's intended destination before sending the file to print takes a moment, and saves all that trouble.
How to handle it before sending the file to print
Before you design anything, answer one question: where will this flyer physically end up. If it's an envelope, measure the envelope, don't guess. If it's a display stand, measure the stand's compartment, ideally with a ruler, not by eye. If it's meant to be handed out directly or read as a standalone document, look at the amount of content, since that's what decides between DL and A5, and sometimes A4 too.
- I physically measured the stand or envelope the flyer is meant to go into, instead of assuming the format by eye
- I checked whether the amount of content fits comfortably in the chosen format without cramming the text
- For an A4 folded into an envelope, I designed the panels separately, with a margin from the fold line
- The file has a 3 mm bleed added on each side, and backgrounds and photos reach the gross edge, not the net one
- Important text and logos sit at least 3-5 mm from the cutting line, not on it
- I matched the paper weight to how the flyer will be used, not just to how it looks on screen
DL, A4 and A5 formats aren't a matter of taste, but of logistics: the envelope has its own dimension, the stand has its own compartment, and the recipient's hand has its own comfort. Match the format to the destination first, and only then play with the graphic layout within its limits - in that order you'll avoid a situation where a finished print run sits in the warehouse because it doesn't fit where it was meant to go.
DL format A5 format A4 format print bleed safety margin flyers prepress
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