Postcard Dimensions UK: A Complete Print and Post Guide

You've finished the artwork, checked the colours and sent the proof around your team. Then, just before placing the order, someone asks a question that should have been answered at the start: what are the finished postcard dimensions, and will Royal Mail treat the piece as a standard Letter?

That question catches out many UK businesses. A postcard can look like a familiar A6 design on screen but become a different postal product after trimming, coating, mounting or adding an attached element. The correct decision connects the artwork canvas, finished trim, paper stock, thickness, weight and mailing format.

Getting the Size Right for Your UK Postcard

A Bristol coffee roaster is preparing a promotional mailing for local customers. The team has produced a bright, image-led design and specified the artwork in millimetres. The front looks right, the QR code scans and the address side has been approved. During the final production check, however, the finished piece is measured with its chosen stock and coating. It no longer fits the team's intended postal category.

That's the point at which a simple design job becomes a fulfilment problem. The visible face may still look like a postcard, but Royal Mail assesses the finished mailed item, not the idea behind the artwork. If the piece exceeds a relevant Letter threshold, the business may need a different service and a revised postage calculation. The risk is especially high when a card is laminated, mounted, unusually rigid or produced on a heavy board.

Practical rule: Choose the postal category before approving the paper and finish, not after the cards arrive.

Postcard dimensions in the UK are therefore part of a chain of decisions:

• Trim size: The dimensions after the printer cuts the sheet.
• Bleed: Extra artwork that extends beyond the trim line.
• Stock: The paper or card selected for stiffness, writing and appearance.
• Finish: Coating, lamination or special treatment that can alter thickness and handling.
• Postal classification: The category that applies to the assembled, ready-to-mail item.

The safest workflow starts with the message and audience, selects a practical finished format, builds the artwork around that trim size, then checks the physical sample. A small event reminder may need a compact card with a clear date and QR code. A menu, map or multi-part offer may need a larger mailer with more usable space.

The sections that follow move in that order, from millimetres and inches to bleed, paper, artwork export and Royal Mail checks. By the end, you'll have a specification for the mailed piece, not merely a document size chosen in Canva or InDesign.

Standard UK Postcard Sizes in Millimetres and Inches

For most UK postcard projects, A6 is the practical standard. Royal Mail identifies the postcard format as approximately 105 × 148 mm, or 10.5 × 14.8 cm, which is approximately 4.1 × 5.8 inches. That alignment makes A6 a useful benchmark for both artwork preparation and finished-format checking. Royal Mail's parcel measuring guidance confirms the recognised postcard dimensions and the wider Letter limits that affect mailing.

Designers normally work in millimetres because print files need precise trim measurements. Customers and campaign teams often think in inches, so keeping both systems visible prevents misunderstandings during approval.

The DL and A5 measurements are useful design references for adjacent mailer formats, but they shouldn't automatically be described as standard postcards. A DL piece is long and narrow, which suits a short offer, loyalty message or display beside other promotional material. A5 gives a team more room for a map, several product details or a catalogue-style introduction.

Square formats create stronger shelf or hand-to-hand recognition, yet their postal treatment needs checking as a finished item. The same applies to any custom size that falls outside the familiar A6 proportions. Before ordering, compare the completed dimensions with the current Royal Mail rules rather than assuming that a postcard-shaped design will receive postcard handling.

For ready-made postcard products and available format choices, review custom printed postcards. Once the trim size is selected, the next job is building the file larger than that finished face so the cutter has room to work.

Setting Up Bleed, Safe Area and Crop Marks

A postcard can leave the designer's screen looking perfect and still arrive with a thin white edge. The usual cause is a background that stops at the finished edge, leaving the cutter no room for small movement. Set up the artwork, paper choice and finished mailed piece together, then check the result before approval.

For a standard A6 postcard, the trim line is 105 × 148 mm. Add 3 mm of bleed on every edge, so the working artwork file measures approximately 111 × 154 mm. The combined bleed adds 6 mm to the overall dimensions. Trimming removes that extra material and leaves the intended 105 × 148 mm face. Use the printer's supplied template for crop-mark placement when one is available.

Keep a 5 mm safe area inside the trim line for names, prices, telephone numbers, QR codes and logos. This margin acts like a buffer between important information and the blade. Extend full-bleed photographs, colour fields and dark backgrounds past the trim line, otherwise a small cutting variation may reveal an unprinted strip.

What each mark does

• Bleed: Extends background artwork beyond the finished edge.
• Safe area: Keeps important content away from the cut.
• Crop marks: Show the cutting position and sit outside the finished design.
• Trim line: Defines the final postcard dimensions.

InDesign, Illustrator or Canva should include the bleed settings rather than stopping at the trim size. A background that ends exactly on the trim line may expose white after cutting, even when the proof appears accurate.

Export crop marks in the printer's requested colour space, commonly CMYK, and keep them separate from the live design. Do not place them over logos or text. Check the completed card, including its stock and finish, because the finished item is what enters the mailstream. If related stationery is part of the campaign, the same preparation principles apply to this business card printing guidance.

Royal Mail Postcard Rules and Postage Thresholds

The key distinction is between the card's physical dimensions and its postal classification. A standard UK Letter can measure up to 240 × 165 × 5 mm and weigh up to 100 g. Royal Mail's current price guidance includes postcards among Letter-format examples, so an A6 card sits comfortably inside the length and width limits when its finished construction also remains suitable. Royal Mail's current UK price guide sets out the Letter thresholds used for this comparison.

Royal Mail addressing guidance also gives a minimum card size of 140 × 90 mm, a thickness range of 0.25 mm to 5 mm and a minimum paper weight of 200 gsm for a postcard or card. These checks help distinguish a mailing card from a lightweight sheet that may not handle reliably in postal processing. The clear addressing guide provides those production-focused requirements.

A heavy stock can increase the finished weight. Lamination can affect thickness. A glued-on token, mounted insert, rounded construction or protective envelope can change how the item is assessed. A folded format may no longer behave like a simple flat postcard, even if one panel resembles A6.

Measure and weigh the piece that will actually enter the postbox. The PDF is not the postal item.

Before a large run, assemble one complete sample with the final stock, coating, adhesive elements and address treatment. Measure its length, width and thickness, then weigh it in its mailing condition. If the dimensions or construction are unusual, confirm the category and current service price with Royal Mail before committing to production. Envelope-based campaigns should also account for the packaging itself. UK printed envelopes can be useful for larger or more private mailers, but they become part of the finished item being checked.

Choosing Between a Postcard and a Larger Mailer

A6 is a strong choice when the campaign has one job. That might be reminding an existing customer about an appointment, directing a visitor to an event page or presenting a single promotional offer. Its compact face encourages editing, which can make the message easier to scan, while its relatively small format can support efficient handling.

A5 gives the message more room. A team can include a short offer, a map, several product images or a tear-off response device without forcing every element into a tight composition. A4 or folded formats provide still more storytelling space, but the extra panels also introduce more folds, handling steps and production decisions.

The right format depends on the objective rather than habit.

Response evidence also argues against assuming that the smallest format always wins. In a specific warm-retail direct-mail sample, JICMAIL's 2025 tracker reported an A5 response rate 2.7 times higher than postcards. The same source reported mail volumes up 5% year on year, average direct-mail attention of 145 seconds, average reach of 1.14 people per household and more than 16% of mail items prompting a household discussion in separate Q1 2025 results. These figures describe particular samples and shouldn't be treated as a universal ranking of formats. JICMAIL's published results are most useful as a reminder to test the format against the campaign objective.

If the message is a reminder, begin with A6. If the customer needs to compare options, understand a route, read a menu or act on several details, consider A5. A larger format earns its place when the additional space improves comprehension or response, not because it looks more substantial. For folded or leaflet-style campaigns, leaflet printing options can provide formats beyond a flat postcard.

Paper Stocks and Finishes That Fit Each Format

Paper selection affects three things at once: how the card feels, how well it performs in use and how it behaves in the postal system. Start with the purpose of the piece, then choose the weight and finish around that purpose.

For an everyday postcard, 250 to 300 gsm is a sensible production range when the card needs to feel firm rather than flop in the hand. A premium direct-mail or loyalty piece may use 350 to 400 gsm for a more substantial feel. These are production recommendations, not guarantees of a postal category. The final sample still needs to be weighed and measured because stock, coating and size work together.

Match the surface to the response

• Uncoated stock: A practical choice for a writable address side, appointment note or hand-completed response.
• Silk stock: Balances image reproduction with a softer surface and restrained sheen.
• Gloss stock: Gives photographs and strong colour a bright, polished appearance, though handwriting may be less comfortable.
• Recycled stock: Supports an earthy, material-led identity and can suit community, food or sustainability messaging.
• Textured stock: Adds tactile character, but fine type and small QR codes need careful proofing.
• Lamination or soft touch: Protects and changes the feel of a surface, while adding another construction variable.
• Spot UV or other raised details: Works best when reserved for a small number of deliberate features rather than spread across every element.

An A6 promotional card often benefits from an uncoated or writable back, especially when the recipient needs to note a date or bring the card to an event. An A5 mailer may make better use of a coated or soft-touch front because it has more visual space for photography and product presentation.

The more material you add, the more important the physical check becomes. A premium finish can increase rigidity or thickness, while heavier stock can raise the total mailing weight. Don't select a finish because it looks impressive on a screen. Ask whether it improves readability, protection, writing, handling or the perceived value of the offer.

For a coordinated business pack, printed stationery can help keep paper choices and finishes consistent across postcards, letterheads and supporting materials.

Artwork File Settings for Clean Print Output

A reliable postcard file is easier to approve because its dimensions, colour and construction are clear. Use this compact checklist before uploading:

1. Set the document to the finished trim size. For A6, that means 105 × 148 mm before bleed is added.
2. Add 3 mm bleed on every edge. Extend backgrounds and photographs into that area.
3. Keep essential content 5 mm inside the trim. This protects text, logos and response elements.
4. Use 300 dpi for raster images at final size. Logos and type should remain vector wherever possible.
5. Choose CMYK. Use FOGRA39 or ISO Coated v2 for coated stock, and ISO Uncoated v2 for uncoated stock when those profiles match the printer's workflow.
6. Control black builds. A rich black of 40/40/40/100 can suit large filled areas, while 100K is usually cleaner for small body text.
7. Embed fonts or outline type. This prevents substitutions when the printer opens the PDF.
8. Keep fine rules at or above 0.25 pt. Hairlines can disappear or reproduce inconsistently.
9. Export as PDF/X-1a or PDF/X-4. Follow the printer's preference if it specifies one.
10. Use a single-page file. Name the file clearly and distinguish front and back versions where needed.
11. Manage spot colours carefully. Give them consistent names and don't leave accidental duplicates in the file.
12. Link images properly. Avoid missing links and pasted objects that behave unpredictably during export.

Check the exported PDF, not only the working file

Open the final PDF in a viewer and inspect it at close scale. Confirm that the document includes the intended bleed, crop marks sit outside the design, images remain sharp and no text has shifted. A preflight panel in Adobe Acrobat Pro or the output preview in Adobe InDesign can identify colour-space, font and overprint problems before submission.

Flatten only when the chosen PDF workflow requires it. Keep an editable master file separately, then make one controlled export for print. The filename should identify the format, side and revision so nobody sends an outdated proof to production.

Preflight Checklist and Design Tips for Maximum Impact

A postcard proof can look correct on screen and still create a problem at fulfilment. The paper, coating, finish, assembled thickness and mailing category all need checking together before the print run is approved.

Use this final handover checklist:

• Confirm the materials: Compare the approved paper stock, coating, lamination and special finishes with the production order. A finish can change the card's feel and thickness.
• Inspect a physical sample: Measure the trimmed card, check its thickness and weigh the assembled mailing item. Include any attached or inserted elements that will travel through the post.
• Verify postage: Compare the complete sample with the intended Royal Mail category before approving the full run. If the finished piece falls into another category, resolve the postage and format decision at this stage.
• Technical settings: Confirm the file already meets the bleed, safe-area, dpi, colour and export requirements in the artwork checklist above.
• Proof at actual size: Read the sample at its finished scale, checking small type, contrast, image detail and the visibility of the response route.

Design hierarchy controls how quickly the message can be understood. Give the front one dominant purpose, such as a seasonal offer, event name or customer benefit. Support it with one clear call to action and make the response route obvious. On a compact card, open space often improves comprehension more than an extra sentence or decorative graphic.

Typography needs a physical check as well as a screen proof. Use 9 pt minimum body copy as a working design recommendation, then read it at finished size. Set strong contrast between text and background, keep important information away from busy photography and leave clear space around QR codes so they can be scanned reliably.

Plan the reverse as a set of working zones. Separate the address area, postage indicia, brand information and response mechanism so each part can be found quickly. This arrangement also leaves the mailing side usable when the card is handled, sorted and delivered.

Treat the checklist as the handover between design and fulfilment. Approval is complete when the assembled sample matches the intended Royal Mail category and the physical result supports the message.

The Print Warehouse Ltd offers custom printed postcards and related marketing materials with online artwork upload, proofing, material choices and finishes for UK businesses and individuals. Prepare the final artwork and physical checks, then visit The Print Warehouse Ltd to review postcard options and submit the print-ready artwork.