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Packaging Guide

Our cardboard boxes (or cartons) are made from corrugated sheets, either in single or double wall construction. We transform these corrugated sheets at the Belmont Packaging factory; cutting, creasing, printing and gluing into the flat-packed stock boxes you purchase. We hold a wide range of stock boxes, with some great price quantity breaks. Don't forget to use our Box Finder to help locate the right box. If you can't find a stock box of a suitable size, why not Contact our sales team to discuss your bespoke options.

In our packaging guide you can explore the following areas;

How to measure your boxes

Understand Royal Mail Parcel Sizes

Understand Board Grade Terminology

Single Wall vs Double Wall

Measuring Boxes

Standard corrugated boxes are always measured in the same order (with the box opening at the top);

The box dimensions, stated by a supplier, refer to the internal (usable) dimensions of the carton. 

Boxed-Up supply a range of various sized boxes, which can seem daunting when you are unsure which size box you need. In order to find the right box for your needs, you will need to determine how large your product(s) will be that you wish to house in the same box.

Firstly we suggest measuring your goods. It is good practice to measure your goods in the same way as manufacturers; Length x width x Height. This will make it easier for you when determining and picking a stock box size. It is also perhaps a good idea to think of other layouts of your products, as this can bring up other stock box options which may be suitable.

When choosing your box remember that bubble wrap, foam chips and other protective packaging material will add to the space needed. They are also great void fillers, if your box is slightly too large. It is best to select a box which is slightly larger in all 3 dimensions to allow room for the protective padding.

Ideally the best packaged goods are those which sit snugly inside the box, meaning minimal movement of your goods during transit.

If you have seen a box which you think may be suitable but are unsure, or perhaps you have a couple of stock box options which could work. Please get in touch with us and the sales team will be happy to assist you where they can.

Understanding the Royal Mail Parcel Sizes

For those smaller ecommerce businesses and hobbyist who ship out their creations through the post, finding the right sized box can be crucial. Not only to ensure that your products arrive to the customer undamaged but that it fits within certain shipping criteria.

As most of you know, the main UK postal system Royal Mail updated their shipping sizing categories and corresponding pay structures. Over 2013 and 2014 they have changed their ‘pricing in proportion’ policy, abandoning its previous ‘packet’ category, to be replaced with two new bands called ‘small parcel’ and medium parcel’.The various changes Royal Mail have made in perfecting the various sizing price structures is to presumably remain in line with the growing online shopping trend.

As a manufacturer these sizes are important to consider, in order for us to create stock boxes which our customers require in order to ship their products within the certain category restrictions.

At present the current category information are as follows;

LARGE LETTER – 353mm x 250mm x20.5mm (750g weight)

SMALL PARCEL – 450mm x 350mm x 160mm (2kg weight)

MEDIUM PARCEL – 610mm x 460mm x 460mm (20kg weight)

Unless you want to keep a tape measure to hand and buy a new box for every different type of box you send out, which can become quite costly. It is beneficial to get your boxes from a trusted supplier who can guarantee that, as long as you remain within the weight restrictions, you can be confident which category your parcel will fall into.

A parcel need only go a few millimetres over the maximum to up your costs considerably. If you’re dispatching twenty 2kg parcels each working day on a 1st class service, using ‘medium parcel’ packaging instead of ‘small parcel’ could cost you an extra £69 a day, or £345 each week.

You can get a plastic guide from the Post Office – if your parcel passes through the relevant slot, you’ll know that it is the right size for that category. But that could be quite a long-winded exercise to do for every single box.

Alternatively you can feel at ease in the knowledge that our following stock box styles fall within the following categories;




Corrugated Board Descriptions

A standard sheet of corrugated board is made with two main components: linerboard and corrugated fluted paper. The sheet of fluted paper is sandwiched between an outside and inner liner which is then glued to the flat liner paper with starch.

When searching for a corrugated case you will generally see a description of the board as B125KT, which is a shorthand description of the board grade, paper weight and fluting size. 

B = fluting Size

125 = Paper weight

KT = Kraft/ Test Paper (Outer/ Inner Liner)

The most common papers used to create stock boxes are a combination of Kraft and Test paper, as detailed above. Kraft paper is made from virgin fibres using softwoods from sustainble forests. The nature of this paper makes this paper the most commonly used outside liner. Test paper is made predominately from recycled papers which give it its mottled effect and is often the most common inner liner used in creating corrugated cardboard. 

It is the size of the flute and the weight of the paper used, which determine the strength and performance of the board, which translate through to determine the same properities of the constructed corugated case. 

All of the listings on Boxed-Up will detail the board grade used for each of our stock and clearance boxes.  If you want to gain a better understanding of the board grade breakdowns supplied from suppliers, read more from our blog.

Single Wall vs Double Wall

Single Wall boxes are constructed utilising one layer of fluting. They are the most commonly used boxes for ecommerce shipping packaging, as they are a cheaper alternative to double wall yet still provide rigidity and cushioned protection required of a shipping carton. Single Wall boxes are reliant on the flute, to determine the properities of that case. For example short flutes such as E, are able to withstand crushing far better than a larger flute. Larger flutes such as B and C are able to absorb more shock and provide a greater cushioned protection, than the smaller flutes, which is why we have chosen this fluting for our single wall stock boxes. 

Double Wall boxes are consrtucted with two layers of fluting, generally in two types of flute sizes. The 5-ply construction provides a greater strength over the double wall, making them the perfect choice for heavier items or items which require a higher level of potection. As like the single wall, double wall boxes have their abilities and properities defined by the type of flute chosen. The increase rigidity over the single wall, makes double wall te ideal choice for utilising in long term storage. We recommend to our customers to use our double wall when shipping heavy items or for long term storage.

Read more about single and double wall on our blog.