UK Print Sizes Explained: ISO 216, A-Series & DL

A4, A5, DL — UK print sizing looks arbitrary until you see the logic. Two minutes here saves you ordering the wrong size or downloading the wrong template.

The A-Series Logic: Every Size Is Half the One Above

The international ISO 216 standard is built on one elegant trick: every A-size has the same proportions (a width-to-height ratio of √2, about 1:1.414), which means folding or cutting any sheet in half gives you the next size down with identical proportions. A0 is defined as one square metre of paper; halve it and you get A1, halve again for A2, and so on.

What Is DL?

DL is 99 × 210mm — exactly one-third of an A4 sheet. It exists so an A4 letter folded in three, or an unfolded compliment slip, slides perfectly into a DL envelope. It's the standard for compliment slips, rack leaflets and tri-fold brochures.

Envelope Pairing (C-Series)

Envelopes run on the matching C-series, each sized to take the same-numbered A-sheet: C4 takes flat A4, C5 takes A5 (or A4 folded once), and DL envelopes take a DL slip or A4 folded in three.

The US Template Trap

US sizes are different: US Letter is 8.5 × 11in (216 × 279mm) — wider and shorter than A4 — and US business cards are 3.5 × 2in (89 × 51mm) vs the UK's 85 × 55mm. If you download a template from a US website, your artwork will be the wrong size for UK printing. Always start from a UK/ISO template — ask us and we'll send the correct one for your product. Browse our full business stationery & publications range.

B-series and SRA sizes: the ones you meet less often

ISO 216 also defines a B-series, which sits geometrically between the A sizes. B5 is 176 × 250mm and B4 is 250 × 353mm. You will mostly see B sizes on posters, some books and paperbacks, and in Japan and parts of Asia, where they are more common than in UK offices. If a supplied brief says "B2 poster", check it is not a typo for A2, because the two are different shapes and the artwork will not scale between them without cropping.

Printers also talk about SRA3 (320 × 450mm). It is a bit larger than A3 and is not an ISO 216 size itself. It exists because printing presses need spare paper around the page for trim, crop marks and colour bars. If your job is A4 or A3 and there is a design that goes right to the edge, the sheet it is printed on is usually SRA3, then cut down to size. You do not need to design on SRA3. Just design at the finished size and add bleed.

Bleed, trim and safe area for each size

A page size is the finished, trimmed size. Artwork needs more than that on the file, or a thin white sliver can appear along the edge when the guillotine moves a fraction.

• Bleed: extend background colour and images 3mm beyond every edge. An A5 leaflet file becomes 154 × 216mm.
• Trim line: the finished edge, where the cut happens.
• Safe area: keep text and logos at least 3 to 5mm inside the trim line, and more on anything that will be folded or bound.

Folded items need extra care. A tri-fold DL leaflet is usually made from an A4 sheet, but the three panels are not always identical, because the panel that tucks inside is often made a millimetre or two narrower so it does not buckle. Ask for the fold template, not just the flat size, before you place text near a crease.

Orientation and how sizes are written

UK printers write size as width first, then height, so 210 × 297mm is portrait A4 and 297 × 210mm is landscape A4. Check the order when you read a quote or fill in a template, because a landscape job entered the wrong way round is one of the most common reasons for a corrected proof. Brochures and calendars are often described as "A4 landscape" or "A5 portrait" for exactly this reason.

Choosing a size for the job

Size choice is partly practical and partly about how the piece will be used.

• A6 and DL: easy to hand over, fit in a pocket, work well for offers, appointment reminders and short messages.
• A5: the usual choice for leaflets that need a bit more room for a menu, a price list layout or a short story about the business, and the standard size for most small booklets.
• A4: the best choice for documents, forms, menus and anything people will fill in or file in a ring binder.
• A3 and above: for things people read from a distance, such as posters, wall planners and shop notices.

A good test is to print your layout at actual size on a home printer and hold it. Text that looks fine on a monitor often turns out too small in A6 or DL.

Scaling artwork between sizes

Because every A size shares the same proportions, a design built for A4 will scale to A5 or A3 without distortion. That is very useful: one master layout can become a poster, a flyer and a postcard. Scaling does change how big the text looks, so check that body copy is still readable at the smaller size and that small print does not shrink below a comfortable reading size. Moving from A4 to DL is different. DL is a different shape, so the layout needs rebuilding, not scaling.

Envelope sizes in more detail

The C-series matches the A-series, but the envelope is slightly bigger than the sheet it holds so there is room to slide it in. C6 is 114 × 162mm and takes A6, or A4 folded twice into quarters. C5 is 162 × 229mm and C4 is 229 × 324mm. The DL envelope is 110 × 220mm and the DL leaflet or a tri-folded A4 letter fits inside it. If you are sending printed pieces by post, decide on the envelope first, then size the print to match, because it is much harder to find a standard envelope for an odd-sized leaflet.

Common sizing mistakes

• Downloading a US Letter template for a UK job, then discovering the proportions are different.
• Setting up a business card at A7 (74 × 105mm), which is far bigger than a normal card. UK cards are 85 × 55mm.
• Forgetting that a folded A5 leaflet opens out to A4, so the artwork needs to be set up as a spread.
• Sending a file in pixels without a stated resolution. A 2480 × 3508 pixel image is A4 at 300 pixels per inch, which is a good guide when you are checking an image for print.
• Designing a booklet at a size that does not divide neatly. Booklets are built from multiples of four pages, so plan your page count to match.

Is A4 exactly 210 × 297mm?

Yes. ISO 216 sets A4 at 210 × 297mm, and the same proportions apply all the way up and down the series. Printers allow a small trimming tolerance of about a millimetre, so a very precise measurement may differ slightly on a finished piece.

What size is a standard UK business card?

Most UK cards are 85 × 55mm. This is not an ISO 216 size, which is why it does not belong to the A-series. If you want a different shape, such as square or slim, tell us at the start so the layout and the cutting can be planned.

Can I print an A3 design on A4 paper?

You can reduce it, because the proportions match, and it fits with no cropping. Check that small text is still readable once it has been shrunk to roughly seventy per cent of the original linear size.