A6 vs A5 Postcards: Choosing the Right Size

Two Sizes, Different Strengths

A6 and A5 are the two most popular postcard sizes in the UK, and for good reason. Both fit within Royal Mail's standard letter pricing, they are easy to design, and they suit a wide range of uses. But they are not interchangeable.

Choosing the right size comes down to what you are saying, how you are distributing, and what you are willing to spend on postage. Here is a straightforward comparison.

The Dimensions

A6 measures 105 x 148mm (roughly 4.1 x 5.8 inches). This is the size of a standard postcard you would send from holiday. It fits comfortably in one hand and slips into a pocket or bag easily.

A5 measures 148 x 210mm (roughly 5.8 x 8.3 inches). That is exactly half of an A4 sheet. It is noticeably larger and gives you about twice the printable area of an A6.

Postage Costs with Royal Mail

Both A6 and A5 can qualify for Royal Mail's standard "Letter" rate, which is the cheapest option. To qualify as a Letter, your postcard must be:

• No larger than 240 x 165mm
• No thicker than 5mm
• No heavier than 100g

An A6 postcard fits within these limits easily. An A5 postcard (148 x 210mm) exceeds the 165mm height limit for a Letter when held in portrait orientation. However, in landscape orientation (210mm wide by 148mm tall), it fits within the dimensions.

In practice, if you are posting A5 postcards, you should be aware that Royal Mail may measure them either way at the sorting office. Some businesses have their A5 cards classed as Large Letters, which costs more. At current rates, a Second Class Letter is 85p while a Second Class Large Letter is £1.29. That difference adds up fast on a batch of 500.

If keeping postage costs as low as possible is a priority, A6 is the safer choice.

How Much Content Can You Fit?

This is where A5 pulls ahead. With roughly double the surface area, an A5 postcard gives you room for:

• Larger images or multiple product photos
• More detailed descriptions or a short menu
• A map or directions to your premises
• A fuller list of services alongside your contact details

An A6 postcard forces you to be concise. You get space for one headline, one image, a short block of text, and your contact information. That constraint is actually useful for things like appointment cards, discount vouchers, and simple calls to action. But if you are trying to explain something or list multiple items, you will find yourself running out of room.

When to Choose A6

A6 works best when your message is short and your budget is tight. Good use cases include:

• Appointment reminder cards
• Discount vouchers and loyalty cards
• Thank-you inserts for online orders
• Simple "we have moved" or "now open" announcements
• Direct mail campaigns where postage cost per unit matters

The smaller size also makes A6 cards easy to display in countertop holders or hand out at events. They are the most ordered postcard size we print here at Belfast Print.

When to Choose A5

A5 makes sense when you need more space or want your card to stand out from smaller mail. Good use cases include:

• Mini menus for restaurants and takeaways
• Event invitations with full details (schedule, map, lineup)
• Product launch announcements with multiple images
• Service listings for tradespeople (plumber, electrician, landscaper)
• Property marketing cards for estate agents

The larger format also looks more serious when someone picks it up, which can work in your favour for higher-value services. If you are comparing other print sizes for marketing, our guide to flyer sizes covers A4, A5, A6, and DL in more detail.

Paper Stock and Finish

Both sizes are available on the same range of stocks. For postcards that will be mailed, a 400gsm card with gloss or matt lamination on one side is the standard choice. It feels sturdy, looks professional, and survives the postal system without getting dog-eared.

If the recipient needs to write on the card (for example, an appointment card or a feedback form), leave one side uncoated or choose a silk finish that takes pen reasonably well.

Quick Comparison Table

• A6 (105 x 148mm): Lower print cost per unit. Fits Royal Mail Letter rate reliably. Best for short messages, vouchers, reminders.
• A5 (148 x 210mm): More content space. May attract Large Letter postage. Best for menus, event invitations, detailed promotions.

Order Your Postcards

We print both A6 and A5 postcards on premium card stocks with a choice of finishes. Turnaround is fast, and we deliver across Belfast and Northern Ireland. Head to our postcards page to pick your size, quantity and finish.