Postcard Size Guide: Choosing the Right Size for Your Postcard

Postcards are pretty simple… until you need to choose a size.

A6 is the standard postcard size in the UK, measuring 148 × 105mm. It’s the familiar format most people picture when they think of a postcard, but it isn’t always the best fit for every job.

Sometimes you need more room. Sometimes a longer shape works better with the artwork. And sometimes a square format just suits the design more naturally.

At StressFreePrint, our postcard range includes A5, A6, DL and 148mm square, so here’s how they compare and where each one tends to work best.

Postcard Sizes at a Glance

Here’s a quick comparison, including the pixel dimensions you’ll need if you’re setting up artwork at 300dpi.

Postcard Size	Millimetres	Centimetres	Inches	Pixels at 300dpi
A6	148 x 105mm	14.8 x 10.5cm	5.83 x 4.13in	1748 x 1240px
A5	210 x 148mm	21 x 14.8cm	8.27 x 5.83in	2480 x 1748px
DL	210 x 99mm	21 x 9.9cm	8.27 x 3.90in	2480 x 1169px
148 Square	148 x 148mm	14.8 x 14.8cm	5.83 x 5.83in	1748 x 1748px

These measurements are for the finished postcard size. If your background colour or image runs right to the edge, you’ll also need to allow for 3mm bleed outside the finished size.

The pixel dimensions are based on artwork prepared at 300dpi. If you’re working at a different resolution, the pixel count will change even though the physical size stays the same.

A6… The Standard Postcard Size

If you’re not sure where to start, A6 is usually the safest option.

At 148 × 105mm, it gives you enough space for a strong image, headline and a small amount of supporting information without feeling oversized.

It works well for things like promotional mailers, event handouts, thank-you cards, appointment reminders and general marketing.

It also feels instantly familiar. People know what to do with it, whether it arrives through the post or gets handed to them at an event.

For a simple message with one clear purpose, A6 is hard to go wrong with.

When A5 Makes More Sense

A5 is exactly twice the area of A6, so you get a lot more room to work with.

That extra space can be useful when the postcard needs to do more than show one image and a short message. You might have several offers to include, a larger photograph, more detailed event information or a call to action that needs a bit more breathing space.

It still feels compact enough to hand out or send, but there’s noticeably more room for the design.

The trick is not to fill the space just because it’s there. If the message is short, A5 can start to feel empty quite quickly.

Choose it because the content needs the room… not simply because bigger feels better.

DL Postcards Work Differently

DL postcards have a longer, narrower shape at 210 × 99mm.

That proportion can work really well for designs that naturally run across the page, especially where you’ve got a wide image, a simple headline or information that can be broken into a few clear sections.

They can also feel a little less expected than A5 or A6 without looking unusual.

The shape does mean you need to think about the artwork differently. A design that looks balanced on A6 won’t necessarily drop neatly onto DL without some rearranging.

If you already know you want a wide, slim layout, DL can be a really useful option.

What About Square Postcards?

A 148 × 148mm square postcard gives you something noticeably different without changing the overall scale too much.

Square formats work particularly well with centred artwork, photography, illustrations and designs where the visual is doing most of the work.

They can also be useful when you want the postcard to feel a little less like a traditional mailer and more like something people might keep.

One thing to watch is the change in proportions. If your artwork was designed for A5 or A6, simply cropping it into a square can easily cut off something important.

It’s usually better to design with the square format in mind from the start.

Portrait or Landscape?

The physical size doesn’t change when you turn a postcard around, but the design can feel completely different.

Landscape tends to work well for wide photography, product shots and layouts where information runs naturally from left to right.

Portrait gives you more height and can work better for invitation-style designs, promotional pieces or artwork where the content stacks down the page.

There isn’t a right answer here. Start with the artwork and the information you need to fit rather than choosing the orientation first and forcing everything into it.

Getting Your Artwork Ready for Print

Once you’ve chosen the size, make sure the artwork actually matches it.

If a background colour or image runs right to the edge, you’ll need 3mm bleed around the finished size. Keep text, logos and anything important safely inside the edge so there’s no risk of them sitting too close to the trim.

For images, 300dpi at the final size is ideal.

This becomes more noticeable when an image is used at a larger size. A photograph that looks perfectly sharp when used small can start to show its limitations when it’s stretched across an A5 card.

If the original image is already low resolution, simply changing it to 300dpi won’t put the missing detail back.

So, Which Postcard Size Should You Choose?

If you want the familiar option, start with A6.

Choose A5 when your content genuinely needs more room, DL when a long narrow format suits the artwork and 148mm square when a balanced square layout works better for the design.

There isn’t one postcard size that works for everything… and there doesn’t need to be.

Start with what you’re trying to communicate, then choose the size that gives it enough room to work properly.

When you’re ready, take a look at our postcard printing options and choose the format that best suits your artwork.