Understanding UK Paper Sizes: A Complete Guide for the Print Industry

by Chris Perry | Nov 14, 2025 | Artwork Tips, Education

When it comes to print projects, understanding paper sizes is fundamental to getting your job right the first time. In the UK, we use the ISO 216 standard (the A-series you’re familiar with), but how does this compare to US sizes, and what do you need to know about envelopes? Let’s break it all down.

The A-Series: The UK Standard

The beauty of the A-series paper sizes lies in their mathematical elegance. Each size maintains the same aspect ratio (1:2), meaning when you fold an A4 sheet in half, you get A5. Fold it again, and you have A6.

Common A-Series Sizes

A0: 841 × 1189mm – Perfect for large format posters and technical drawings
A1: 594 × 841mm – Ideal for flip charts and architectural plans
A2: 420 × 594mm – Popular for posters and display boards
A3: 297 × 420mm – Used for tabloid-size documents and small posters
A4: 210 × 297mm – The standard office paper size in the UK
A5: 148 × 210mm – Common for notepads, flyers, and small brochures
A6: 105 × 148mm – Perfect for postcards and small leaflets
A7: 74 × 105mm – Typically used for small notepads and business cards

Why the A-Series Matters in Print

For printers, the A-series system is incredibly efficient. Because each size is exactly half of the previous one, we can optimize paper usage and minimize waste. When printing A5 flyers, we can fit two on an A4 sheet. Four A6 postcards fit perfectly on A4. This standardization makes production planning straightforward and cost-effective.

The consistent aspect ratio also means designs scale beautifully across different sizes without distortion – crucial for maintaining brand consistency across various print materials.

UK Envelope Sizes

Envelopes follow a complementary system, with C-series envelopes designed to hold unfolded A-series paper:

C-Series Envelopes (for unfolded documents)

C6: 114 × 162mm – Holds A6 paper unfolded (perfect for greeting cards)
C5: 162 × 229mm – Holds A5 paper unfolded or A4 folded in half
C4: 229 × 324mm – Holds A4 paper unfolded (standard business envelope)
DL: 110 × 220mm – The most common business envelope, holds A4 folded in thirds

Why DL Envelopes Dominate

The DL (Dimension Lengthwise) envelope is the workhorse of UK business mail. It’s designed to hold an A4 sheet folded into three equal parts, making it ideal for letters, invoices, and statements. It’s cost-effective to post and fits comfortably through standard letterboxes.

UK vs US Paper Sizes: The Key Differences

Here’s where things get interesting – and potentially confusing if you’re working with international clients.

US Letter vs A4

The most common comparison is between US Letter (8.5 × 11 inches or 216 × 279mm) and A4 (210 × 297mm).

A4 is narrower but taller than US Letter
A4 has 6% more surface area than US Letter
Documents designed for US Letter may have margins cut off when printed on A4

Other US Sizes

US Legal: 8.5 × 14 inches (216 × 356mm) – No direct UK equivalent
US Tabloid: 11 × 17 inches (279 × 432mm) – Roughly similar to A3 but different proportions
US Executive: 7.25 × 10.5 inches (184 × 267mm) – Falls between A4 and A5

The Practical Impact

For UK printers working with international clients, these differences matter significantly:

Design considerations: A brochure designed for US Letter won’t fit perfectly on A4 without adjustment
Binding and finishing: Different proportions affect how documents fold, bind, and finish
Envelope compatibility: US #10 envelopes (the equivalent of our DL) are slightly different in size
Print equipment: Most UK print equipment is optimised for A-series sizes

B-Series: The Middle Ground

There’s also a B-series, which sits between A-sizes and is less commonly used but valuable for specific applications:

B5: 176 × 250mm – Popular for books and smaller publications
B4: 250 × 353mm – Used for newspapers and oversized documents

B-series sizes are particularly useful when A-sizes are slightly too small or too large for your needs.

Practical Tips for Print Projects

For Designers

Always confirm whether your client needs UK or US sizes before starting
Build in an appropriate bleed (typically 3mm in the UK) for all sizes
Remember that A-series sizes scale proportionally – design once, adapt easily

For Businesses

Stick to standard sizes wherever possible to minimize costs
A5 flyers are cost-effective because two fit on an A4 sheet
DL envelopes offer the best value for business correspondence
Consider A6 postcards for direct mail – they’re eye-catching and economical

For International Projects

Always specify measurements in both metric and imperial
Check envelope compatibility if mailing internationally
Consider your audience’s expectations – US clients expect Letter size
PDF files should specify page dimensions to avoid confusion

The Environmental Advantage

The mathematical precision of the A-series system isn’t just elegant – it’s environmentally responsible. The ability to cut multiple smaller sizes from larger sheets with minimal waste means less paper in landfill and more efficient use of resources. At Corsham Print, our FSC certification combined with the efficiency of A-series sizes helps us minimise environmental impact while delivering quality print.

Conclusion

Understanding paper sizes might seem like a small detail, but it’s fundamental to successful print projects. The UK’s A-series system offers efficiency, scalability, and environmental benefits that make it the global standard outside North America. Whether you’re printing business cards, brochures, or large format posters, knowing your A4 from your US Letter – and your C5 from your DL – ensures your project runs smoothly from design to delivery.

Need help choosing the right paper size for your next print project? Get in touch with our team at Corsham Print – we’re here to make sure your print works perfectly, every time.

DOWNLOAD PAPER SIZE GUIDE

Crops and Bleeds

by Chris Perry | Feb 10, 2021 | Artwork Tips

Today is the big day. After months of blood, toil, sweat and tears; you’re finally ready. This is your magnum opus, the boldest undertaking of your life, an endeavour that many called you crazy for. It has just been sent off to the printers. You spent what felt like a millennium picking out the perfect paper grammage and size, A5 with 180gsm. A cute little number with a gloss coating that reflects the light in such a way that you’d have to fight magpies for its shine. You’re proud of your work.

You receive an email from the printer. Heart racing you hesitate to open it. Could something have gone wrong? Slowly you take a peek, and the words that show will haunt you for the rest of your days.

“Please include crop marks and 3mm bleed.”

What are Crops?

In printing, crops (commonly known as crop marks) are a set of marks that define the boundaries of a printed area. Crop marks are thin lines placed around the corners of a document and they tell the printer where to trim the paper. As many print jobs need to be trimmed to exact dimensions, the crop marks indicate where the document will be cut.

The image shows an example of where crop marks can be used. A printer will trim the document to the finished size using a guillotine or, in some cases, scalpels or scissors. Once the line between the marks has been trimmed, the document will be the required size.

In general the measurements for crop marks range from 3mm to 5mm in length and are offset by 2-3mm to ensure they they are not visable on the finished product

What are Bleeds?

To have bleed on a document means that the printed design is intending to extend to one or more of the edges of the document. It ensures that when the document is trimmed, the design goes to the very edge of the page. As no printer is perfect and there are slight variations in trimming. If you were to not have any bleed on your design, you could be left with white strips along the edges of the finished project.

There is a distinction between two types of bleeds. The full bleed means that every element of your document will exceed its actual frame whereas the partial bleed means that only some elements of your document will go beyond the layout of your document. This illustration shows a full bleed on a document. This will ensure that when trimmed down, the finished project will have clean borders without white stripes.

The standard measurement for bleed is 3mm to 5mm or more when considering large format out put.

Working Together

Crops and bleeds ensure the quality of your printed documents. Below is an example of what happens when you combine crops and bleeds.

When you create a document that will be printed, crops and bleeds are essential elements to ensure that your final document retains a professional look. This is why you may receive emails asking you to add it to your files. In the above picture, when effectively used, the final finished document (shown in black) will be a nearly perfect size with zero white stripes around its edge.

Regardless if the document has bleed or not, any print job that needs to be trimmed to size will require crop marks. These can be applied using the same software used to create your design. Printers typically print on paper that is larger than the actual document size, for example paper sized SRA3 (450mm by 320mm) would be used for printing documents that aim to be A3 (420mm by 297mm) in size. This extra size allows for the printing of crops marks and bleeds.

Creating Crops and Bleeds

The following post will show you how to add crop and bleed in the commonly used design programs.

Adobe Photoshop

Adobe InDesign

Quark Xpress

Step 1 – Create the document

Begin by creating a new document in Photoshop to the trim size (final size) and resolution that you need. Make sure that rulers are displayed by choosing View > Rulers, and also make sure that snapping is enabled by choosing View > Snap. Click on the ruler and drag a guide to the edge of the document. The guide should snap to the edge of the document automatically. Do this for all four sides of the document.

Step 2 – Create space for the bleed

Now increase the image size (document size) to the size of the project including the bleed. Using some basic maths, you can determine that if your desired bleed amount is 5mm on all four sides, simply add 5mm to each dimension. To achieve this, choose Image > Canvas Size and change to dimensions to the correct amount. Make sure that the anchor at the bottom of the dialog box is set to the centre to force the document to add pixels from the middle out.

When you’re finished, you should end up with a document that is to the bleed size of your final project and guides indicating where the document will trim.

Step 3 – Add the trim marks

The file that we’ve created so far is pretty much all the printer should need. However, there might be times for one reason or another, that you’ll want trim marks that go along with the file that indicate exactly where the project should be trimmed.

To do this you will need to choose Image > Canvas Size and enable the relative button. Enter 30mm in the Width and Height dimensions and click OK. This will expand the canvas by an additional 30mm in both dimensions. Create a new layer for your marks and create a selection in the corner areas of the image using the Rectangular Marquee tool. You can do all four corners at the same time.

With the selections active, choose Edit > Stroke and apply a 2px stroke to the active selections. Deselect the active selections and hide your guides to view the crop marks applied to the project.