Postal Boxes: How to Choose the Right Box for Posting Products

29th Sep 2026

Choosing a postal box sounds simple. Find a box your product fits inside, pack it and send it.

But there's a difference between a product simply fitting inside a box and choosing a box that's actually a good fit.

Too small and you might not have enough room to protect the product properly.

Too large and you can end up filling unnecessary empty space, using more protective packaging and storing boxes much bigger than you actually need.

Then there are other questions.

Should you choose a postal box or a conventional cardboard box?

What size do you need?

Does the colour matter?

What about Royal Mail, Evri and other couriers?

And when does it make sense to move from a stock postal box to something custom-sized?

Here's how to choose.

What Is a Postal Box?

A postal box is a cardboard box designed for sending products through the post or a parcel delivery network.

Many postal boxes use a die-cut design with an integrated lid and tuck-in flaps, rather than the separate top and bottom flaps you'll find on a conventional FEFCO 0201 cardboard box.

At ASC Direct, many of our stock postal boxes use the FEFCO 0427 design.

They're supplied flat-packed and can be quickly assembled when required.

This makes postal boxes particularly popular for:

Ecommerce orders
Clothing and accessories
Gifts
Cosmetics
Electronics
Books and stationery
Subscription products
Handmade products
Marketplace sellers
Smaller retail products

But there isn't one universal postal-box size.

The right box depends on what you're actually sending.

What's the Difference Between a Postal Box and a Shipping Box?

The terms are often used interchangeably.

In everyday language, a postal box is simply a box being used to send something.

But when buying packaging, postal box often describes the familiar die-cut ecommerce-style box with an integrated lid.

A conventional shipping box is more likely to be a FEFCO 0201-style carton, with top and bottom flaps that are normally secured using packaging tape.

Neither is automatically better.

A postal box can provide a neat presentation and quick packing process for smaller products.

A conventional 0201 can be an extremely practical and economical solution for larger, heavier or more varied products.

Start with the product rather than the name of the box.

What Size Postal Box Do I Need?

Start by measuring your product.

You need its maximum:

Length × Width × Depth

Then consider what else needs to fit inside the box.

Does the product need:

Protective wrapping?

Paper cushioning?

An insert?

Tissue paper?

Instructions?

A thank-you card?

Multiple components?

Don't measure the product and automatically order a box with exactly the same dimensions.

You need enough space to pack it comfortably and provide whatever protection it genuinely requires.

But don't go too far in the other direction either.

The objective isn't to find the biggest postal box your product fits inside.

It's to find the smallest appropriate box for the complete packed product.

Are Postal Box Measurements Internal or External?

This is important.

Packaging suppliers may specify boxes using internal dimensions, external dimensions or both.

Never assume.

Internal dimensions describe the usable space inside the box.

External dimensions describe the overall size of the finished parcel.

If you're working out whether your product will fit, you need to understand the internal dimensions.

If you're checking whether the parcel meets a courier's size restrictions, the external dimensions become important.

Corrugated cardboard has thickness, so the two aren't the same.

A box with internal dimensions of:

350 × 250 × 150mm

will be larger than those dimensions externally.

If you're unsure how cardboard boxes are measured, read our guide to internal vs external cardboard box dimensions before ordering.

Don't Choose a Postal Box Based Only on the Courier's Maximum Size

This is an easy mistake to make.

Imagine a courier allows a parcel up to a particular maximum size.

That doesn't mean you should automatically buy a box at that maximum size.

Those measurements are a limit, not a recommendation.

If your product only needs a box half that size, use a smaller box.

Why?

Because otherwise you may be:

Storing a larger box.

Using more cardboard.

Adding more void fill.

Using more protective packaging.

Giving the product more space to move.

And potentially creating a parcel that's more cumbersome than it needs to be.

Start with your product. Then check that the finished parcel meets your courier's requirements.

Not the other way around.

Small Postal Boxes

Small postal boxes are particularly useful for ecommerce businesses.

Typical products might include:

Jewellery.

Cosmetics.

Small electronics.

Phone accessories.

Collectables.

Small gifts.

Craft products.

Stationery.

Spare parts.

A compact postal box can create a neat parcel without requiring large quantities of void fill.

But even within the category of "small postal boxes", dimensions vary considerably.

A long, thin product and a short, deep product might have a similar volume but need completely different boxes.

That's why you should always work from actual dimensions rather than simply searching for small, medium or large.

Large Postal Boxes

The same principle applies to larger products.

As the dimensions increase, you should pay increasing attention to:

Board strength

Product weight

Box rigidity

How the product is supported

How the parcel will be handled

A larger box creates larger unsupported cardboard panels, which can behave differently from a compact postal box.

At some point, a traditional Single Wall, Double Wall or Heavy Duty shipping carton may become more appropriate than a conventional die-cut postal box.

Don't choose a postal-box style simply because you're sending the product through the post.

Should I Use a Postal Box for Royal Mail?

You can use suitable cardboard packaging when sending many products through Royal Mail, provided your parcel meets the relevant service requirements and the contents are packaged appropriately.

But there's an important distinction:

A box doesn't become a Royal Mail box simply because its dimensions fit within a Royal Mail parcel category.

The right packaging still depends on the product.

If you're trying to stay within a particular Royal Mail size category, check the finished external dimensions of your packed parcel.

This is especially important if you're having a box custom-made.

Our Box Builder uses internal dimensions, whereas carrier size limits generally relate to the finished parcel.

For more detail, read our guide to choosing the right-sized box for Royal Mail parcels.

What About Evri, DPD and Other Couriers?

The same principle applies.

Don't begin by asking:

"What's the biggest box this courier allows?"

Ask:

"What size box does my product actually need?"

Then make sure the finished parcel fits the size and weight requirements of the delivery service you've selected.

Different carriers and services have different restrictions, so check the current requirements before sending.

This is particularly important if your parcel is close to a maximum size or weight threshold.

Should a Product Move Inside a Postal Box?

Ideally, your product shouldn't be able to move around excessively during normal handling.

If you can hear or feel it moving significantly when you gently handle the packed parcel, you may need to reconsider the internal protection or box size.

But the answer isn't always to choose a tighter box.

Fragile products need enough space for appropriate cushioning.

Think of it this way:

Too much space can allow excessive movement.

Too little space can leave insufficient room for protection.

The right-sized box sits between the two.

How Much Void Fill Should I Use?

Use enough protective packaging to protect and secure the product.

Not enough can leave the item vulnerable.

But if you're regularly filling half the box with paper, air pillows or another void-fill material, ask a different question:

Is the box too big?

Void fill should solve a genuine protection requirement.

It shouldn't simply compensate for consistently oversized packaging.

This is where right-sized packaging can make a significant difference.

Postal Box or Padded Envelope?

Not every product needs a cardboard box.

A suitable mailing envelope or bag may be perfectly adequate for some lightweight, non-fragile products.

For example, certain:

Clothing.

Documents.

Soft goods.

Textiles.

Low-risk items.

may not require the rigidity of a cardboard box.

A postal box becomes more useful when the product benefits from greater structural protection.

This could include items that:

Can be crushed.

Have vulnerable corners.

Need to retain their shape.

Contain several components.

Require a more structured presentation.

Again:

Don't use a cardboard box simply because you can. Use it because the product needs one.

Postal Box or FEFCO 0201 Cardboard Box?

This is another useful comparison.

A FEFCO 0427-style postal box can provide a tidy integrated-lid design that's quick to assemble and works particularly well for many ecommerce products.

A FEFCO 0201 box is the familiar shipping carton with flaps meeting at the top and bottom.

0201 boxes are extremely versatile and can be manufactured in a very wide range of sizes and board strengths.

Which should you choose?

For a relatively small ecommerce product where presentation and quick assembly matter, a postal box can be an excellent solution.

For a larger, heavier or unusually dimensioned product, a 0201 or another corrugated box style may make more sense.

Choose the structure around the product – not the other way around.

Brown, White or Black Postal Boxes?

Colour doesn't determine whether the box will protect your product properly, but it can influence presentation.

Brown Postal Boxes

Brown corrugated cardboard provides the familiar natural packaging appearance.

It's practical, simple and works well for businesses where elaborate presentation isn't necessary.

White Postal Boxes

White boxes can provide a cleaner appearance and can work particularly well with branded labels, stickers and printed elements.

Black Postal Boxes

Black postal boxes create a distinctive appearance and can suit brands looking for a darker or more premium presentation.

But don't let appearance become more important than function.

The right size and appropriate protection should come first.

Then choose how you want the parcel to look.

What About Printed Postal Boxes?

Your shipping packaging can also become part of the customer experience.

Printed postal boxes can carry:

Your logo.

Brand colours.

A marketing message.

Instructions.

Social media details.

Or other design elements.

This can be particularly useful for ecommerce businesses where the parcel is one of the few physical interactions between the customer and the brand.

But printed packaging isn't essential.

A well-sized plain brown box that protects the product properly is still good packaging.

Branding is an additional consideration – not a substitute for getting the basics right.

Postal Boxes for Ecommerce Businesses

Postal boxes are particularly well suited to ecommerce because they can combine:

Product protection

Quick assembly

Neat presentation

Flat-packed storage

Simple packing

If you regularly send the same products, it's worth standardising the packaging process.

Instead of choosing a different box for every order, decide:

Which product goes in which box?

How much protection does it need?

Where is that packaging stored?

How quickly can someone assemble and pack it?

What happens when order volumes increase?

Saving a few seconds on one parcel doesn't sound important.

Saving those seconds across hundreds or thousands of parcels can be.

Postal Boxes for Etsy, eBay and Marketplace Sellers

Smaller online sellers often have a slightly different challenge.

Storage space may be limited.

You may be packing orders from:

A small workshop.

A spare room.

A garage.

A studio.

Or even the kitchen table.

Buying enormous quantities of multiple postal-box sizes isn't always practical.

That's why it's particularly important to identify a small number of sizes that cover your most common products efficiently.

If you regularly sell the same product, a custom-sized box may also become worth considering.

Stock Postal Boxes or Custom-Sized Boxes?

ASC Direct sells stock postal boxes in a range of sizes.

And if one fits your product properly:

Use it.

Stock packaging can be extremely cost-effective because identical boxes are manufactured in larger quantities.

There's little point manufacturing a custom box purely for the sake of calling it custom.

But suppose your product measures:

280 × 180 × 80mm

and the most practical stock box available to you is:

350 × 250 × 150mm

The product fits.

But you've also created a significant amount of empty space.

If you send that product once, it probably doesn't matter much.

If you send it hundreds or thousands of times, it might.

That's when it's worth comparing a made-to-measure box.

When Should I Consider a Custom Box Instead?

Custom-sized packaging becomes particularly interesting when:

You're regularly using too much void fill.

You're cutting stock boxes down.

Your product moves excessively inside its current box.

You can't find an appropriate stock size.

Your product has unusual dimensions.

You're repeatedly sending the same product.

Storage space is limited.

Or you simply want a more consistent packing process.

ASC Direct's online Box Builder allows you to create corrugated cardboard boxes to your required internal dimensions from just 25 boxes.

That doesn't mean custom is always better.

It means you have another option when stock packaging doesn't fit.

Does a Custom Box Have to Look Like a Postal Box?

No.

This is worth understanding.

If you're searching for "postal boxes", you might assume you need the familiar integrated-lid postal-box design.

But what you actually need is:

A suitable box for posting your product.

That might be a postal-style box.

It might be a FEFCO 0201.

It could be an overlapping-flap 0203.

For a flat product, a wrap-style box might make more sense.

The fact that you're sending something through a courier doesn't dictate the FEFCO style.

The product should.

How Strong Should My Postal Box Be?

Choose a board specification appropriate to:

Product weight

Box dimensions

Fragility

Product shape

Journey

Storage

A small lightweight product doesn't automatically need Double Wall cardboard simply because it's travelling through a parcel network.

Likewise, a very large or long product might benefit from greater rigidity even if it isn't particularly heavy.

The correct box strength is about more than weight alone.

If you're unsure, read our guide to Single Wall vs Double Wall cardboard boxes.

Can Postal Boxes Help Reduce Packaging?

They can – when they're appropriately sized.

A smaller suitable box can mean:

Less unnecessary cardboard.

Less unnecessary void fill.

Less storage space.

And a more compact finished parcel.

But don't reduce packaging to the point where the product is no longer adequately protected.

Replacing an oversized box with an appropriately sized one makes sense.

Removing cushioning from a fragile product simply to use less packaging doesn't.

Use the right amount of the right packaging.

A Simple Postal Box Checklist

Before ordering, ask:

What are the product's maximum dimensions?
How much protection does it genuinely need?
What internal box dimensions will accommodate both?
Is a postal-style box the best structure?
Is the board strong enough for the product?
Will the finished external parcel meet my courier's requirements?
Am I creating unnecessary empty space?
Does the product move excessively when packed?
How many boxes do I need to store?
Would a stock box or custom-sized box make more sense?

If you can answer those questions, choosing packaging becomes much easier.

Frequently Asked Questions About Postal Boxes

What are postal boxes?

Postal boxes are cardboard boxes suitable for sending products through postal and parcel delivery networks. The term commonly describes die-cut ecommerce boxes with integrated lids, although conventional corrugated shipping cartons can also be used for posting products.

What size postal box do I need?

Measure the maximum length, width and depth of your product and allow sufficient additional space for any cushioning or protective packaging it requires. Choose the smallest appropriate box rather than simply the smallest box the product can physically fit inside.

Are postal box dimensions internal or external?

It depends on the supplier, so always check. Internal dimensions describe the usable space inside the box, while external dimensions describe the overall finished parcel size.

Can I use my own cardboard box for posting?

For most normal parcel services, suitable packaging can be used provided it complies with the carrier's current size, weight, packaging and contents requirements. Always check the requirements of the specific service you're using.

What's the difference between a postal box and a cardboard box?

A postal box is a type of cardboard packaging intended for sending products. The term often refers to an integrated-lid die-cut box, whereas a conventional cardboard shipping carton such as FEFCO 0201 normally uses top and bottom flaps secured with tape.

Are postal boxes suitable for ecommerce?

Yes. Postal boxes are widely used for ecommerce because they're supplied flat-packed, relatively quick to assemble and can provide both protection and a neat presentation.

Should I use a postal box or mailing bag?

It depends on the product. Soft, lightweight and non-fragile products may be suitable for an appropriate mailing bag, while products that can be crushed, damaged or deformed may benefit from the structural protection of a cardboard box.

Can postal boxes be customised?

Yes. Custom packaging can be manufactured to suit particular dimensions, products and branding requirements. ASC Direct's Box Builder also allows businesses to order custom-sized corrugated boxes from quantities as low as 25.

Do I need void fill in a postal box?

That depends on the product and how well it fits. Fragile products may require cushioning regardless of box size. If you're regularly using large amounts of void fill purely because the box is oversized, it may be worth choosing a smaller stock box or custom-sized packaging.

Which is better: a stock postal box or a custom box?

Neither is automatically better. If a stock postal box fits your product properly and provides the protection you need, it can be an economical choice. Custom packaging becomes more attractive when available stock sizes create unnecessary space or don't suit the product.

Find the Postal Box That Fits Your Product

There are hundreds of different postal and shipping boxes available.

That's useful.

But don't start by asking:

"Which box can I make my product fit into?"

Start with:

"What does my product actually need?"

Measure it.

Consider the protection it requires.

Choose an appropriate box style and strength.

Check the finished parcel against your courier's requirements.

Then decide whether an existing stock postal box does the job.

If it does: