Mail Parcel Sizes

A Guide to Understanding Mail Parcel Sizes


Over the years, the big mailing systems in the UK have gone through a lot of changes regarding mail parcel sizes. The Royal Mail have made considerable changes, transforming old packet categories into two new size brands, called ‘small parcel’ and ‘medium parcel’. We now have access to lots of different packaging options for our mail too. For example, printed mailing bags, recyclable enveloped, postal bags and more. 

The changes to mail parcel sizes often happen quite quickly without much time to plan for new pricing structures. Consequently, this led to sudden increases in delivery charges for many mail companies. Due to the disappointment among consumers, once again, Royal Mail made two further changes to the small and large parcel specifications over the course of the following year. Now, the Royal Mail’s parcel specifications are quite straight forward.  This article aims to clarify it for you. 

Mail Parcel Sizes in the UK:


  • Up to 240 x 165 x 5mm
  • Maximum weight: 100g

Large Letter

  • Up to 353 x 250 x 25mm
  • Maximum weight: 750g

Small Parcel

  • Up to 450 x 350 x 160mm
  • Or a tube up to 450mm long with a diameter up to 80mm
  • Maximum weight: 2kg

Medium Parcel

  • Up to 610 x 460 x 460mm
  • Or a tube where the length plus twice the diameter must not exceed 1040mm, with the greatest dimension being no more than 900mm
  • Maximum weight: 20kg

Despite all the changes that have occurred over the years, one thing has remained constant. That is that you must be careful in your choice of packaging. For example, one object could be packaged in two different ways and sent successfully. However, the two methods of packaging may have a large cost difference. Therefore, it’s important to choose the most practical and affordable option of packaging for what you are sending. 

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Packaging & Parcel Costs:

Packaging is also key for mail parcel sizes. One of the main tips for choosing the right mail parcel size is getting your postal packaging from a supplier who can guarantee that, if you don’t go over the specified weight for your category, you can be confident which category your parcel falls into.

For example, if your packaging goes over the maximum size category by millimetres, your costs can go up considerably. For example, with Royal Mail, 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.

Royal Mail offers plenty of guides, such as their plastic guide, which lets you see if your parcel will pass through the relevant slot. This reassures you that it is the right size for that category. Alternatively, before ordering your bags and boxes for your next mailout, see if your packaging supplier can provide packaging that has been ‘post checked’ to make sure it meets the Royal Mail Large Letter or Small Parcel sizes.


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