If your business ships by courier or pallet, your cardboard shipping boxes are doing a lot of quiet work. They protect your stock, decide what you pay per parcel, and shape the first impression your customer gets when the delivery lands.

Get the box wrong and it costs you. Too big and you pay for air and void fill. Too weak and you pay for damages and returns. Then, if too heavy or too long, the courier slaps on a surcharge.

This guide explains how to choose the right cardboard shipping boxes for B2B shipping. It covers size and strength, courier limits, and smart use of void fill. It also explains why used boxes work well for high-volume shippers.

How to choose the right size cardboard shipping box

The right box is the smallest one that fits your product plus enough room for protection. Not the one that happens to be on the shelf.

Start with your product’s dimensions, then add space for whatever cushioning it needs. As a rough guide, allow around 2 to 5cm on each side for fragile items, and less for robust goods that just need to stop sliding about.

Internal vs external dimensions

Box sizes are usually listed as internal dimensions (the space you can actually use), written as length x width x height. Courier limits are based on external dimensions. Double wall board adds roughly 1cm to each side, so a box that fits your product perfectly on paper can tip you over a courier limit once it’s built.

Why oversized boxes cost you

• Higher shipping costs. Many couriers price on volumetric weight as well as actual weight, so a big light parcel can cost the same as a small heavy one.
• More void fill. Every bit of empty space needs filling, which is more material and more packing time.
• More damage. Products have room to move, and loosely filled boxes are more likely to crush.
• Wasted pallet and van space. Oversized boxes stack poorly and take up room you’re paying for.

Standardise where you can

If you ship a wide product range, aim for a small core set of box sizes that cover most of your orders. It makes buying simpler, speeds up packing, and makes it much easier to buy in bulk.

How to choose the right strength

Size gets the product in the box. Strength gets it to your customer in one piece. The right strength depends on what’s inside, how heavy it is, and how rough the journey will be.

For most businesses shipping through a courier network, double wall boxes are the safe default. Parcels get handled many times between collection and delivery, and the extra rigidity protects against knocks and crushing.

Three things that affect strength

• Weight of the contents. Heavier products need stronger board, especially near courier weight limits.
• Stacking. If boxes will sit on pallets or in storage, the bottom box carries everything above it. Think about stacking strength, not just what’s inside. Stackable shipping boxes are built for this.
• Condition of the box. A crushed corner or soft, damp board loses strength fast. Whatever you buy, check boxes are dry, square and intact before you pack them.

Pallet shipping

If you ship on pallets, your boxes become building blocks. Choose sizes that fit neatly on a standard UK pallet (1200 x 1000mm) without overhang, stack boxes corner to corner so the weight runs down the strongest part, and stretch wrap the load, so it moves as one unit. For bulky or heavy loads, heavy duty pallet boxes do the job in one go.

Typical UK courier limits

The figures below are a starting point for standard UK services. Limits vary by service level and account type, and they do change, so always check your courier’s current terms before you choose box sizes.

Watch out for volumetric weight

Many couriers charge on whichever is higher: the actual weight or the volumetric weight (based on the box’s dimensions). A big, light box can cost far more than you expect. This is another reason to keep box sizes as tight as your product allows.

Void fill: how much, and what to use

Void fill stops your product moving around inside the box. Movement is what causes most transit damage, so this matters as much as the box itself.

The golden rule: the right size box needs less void fill. Fix the box first, then fill what’s left. For a deeper dive, read our guide on how to choose the right void fill for your business.

Common void fill options

• Paper void fill. Crumpled or folded kraft paper. Widely recyclable and easy for customers to deal with.
• Shredded cardboard. A great use for boxes that are past their best. Good cushioning for robust items.
• Air pillows. Light and quick to use, but plastic-based, so less popular with sustainability-minded customers.
• Corrugated inserts and dividers. Ideal if you ship the same products repeatedly and want a snug, consistent fit.

A quick test

Once the box is packed and closed, give it a gentle shake. If you can hear or feel anything moving, add more fill. If the box bulges or won’t close flat, you’ve overfilled it or the box is too small.

Why used cardboard shipping boxes make sense for high-volume shippers

If you’re sending hundreds or thousands of parcels a month, the boxes you buy add up fast. In cost, and in impact. Used boxes are one of the simplest ways to bring both down without changing how you pack.

Lower cost per box

Used boxes can be up to 50% cheaper than buying the equivalent new. For high-volume shippers, that saving repeats on every order and every restock.

Reuse beats recycling

Recycling is good. Reuse is better. Recycling a box means pulping it, processing it and manufacturing it into something new, all of which uses energy, water and transport. Reusing a box skips all of that and keeps it doing the job it was made for.

Many of the used boxes we supply at Reuseabox come from FMCG manufacturers, where they’ve done one short journey before arriving with us. Plenty of life left in them.

Quality checked, not a gamble

A common worry about used boxes is consistency. At Reuseabox, every box is collected, inspected and quality checked before it’s resold, so you know what you’re getting. Since 2015, we’ve helped UK businesses reuse over 15 million boxes.

A story your customers care about

More B2B buyers are asking suppliers about their environmental impact. Shipping in used boxes is a visible, practical step you can point to, and one your customers will see the moment their order arrives.

Ready to rethink your shipping boxes?

Whether you need a pallet of used double wall boxes, , or help working out which sizes suit your products, we’re here to help. Browse our used cardboard boxes or get in touch with the team for a bulk quote.