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Royal Mail Size Guide

No matter what products you sell online, you can make huge savings on your postal costs by ensuring the parcels you send are as small as they can be. We stock specially designed postal packaging to help you keep your items within the lowest price bands offered by Royal Mail and minimise your parcel volumes with other courier services.

If your packages are bigger than they need to be, you could be paying around 40% more per item. Your packaging choice is the most important factor in getting the best value on your postage so we’ve put together this guide to ensure you always pay the lowest possible postal prices.

Using Royal Mail

The Royal Mail item size guide enables you to check which Price in Proportion category your package fits into.

Royal Mail divides its price bands by Letter, Large Letter, Small Parcel and Medium Parcel which are priced in proportion to the dimensions and weight of packages—the smaller your parcel, the less you’ll pay to send it.

Using Royal Mail

The table below shows Royal Mail Price in Proportion categories.


A letter can be sent using just one first or second class stamp, so sending items as a letter is a great way to save. Use the smallest envelope you can for your document or item – envelopes up to and including C5 size can be sent as a letter with up to 34% savings over the Large Letter prices.

*Saving tip* – Fold your A4 documents in half to fit them into C5 envelopes and if they are no more than 5mm thick and under 100 grams they qualify as a standard letter.

Large Letter

As the size and weight limits are generous – 25mm depth and up to 750g weight – it’s helpful to think of Large Letter as ‘smaller parcel’. Hundreds of products can be packaged to be sent in the Large Letter price bracket, and you can save up to 27% over the Small Parcel prices.

Small Parcel

You can save around 39% on your postal costs with Royal Mail by sending the 1kg – 2kg items you currently send as Medium Parcels as Small Parcels and we’ve got a wide choice of postal packaging products that make it possible.

Medium Parcel

As Royal Mail’s weight limit for Small Parcel is 2kg, parcels weighing more – up to 20kg – are categorised as Medium Parcels. However, once the parcel weight exceeds 1kg, we recommend comparing the prices offered by courier services, as you may be able to get a better price.

Top Tip – Courier Services

If you have a high-volume despatch operation, courier services will most likely be the most cost-effective option for your despatches and keeping the size of the packages you send to a minimum will help you save. You’ll find if you take the long-term approach, building a relationship based on loyalty, you’ll be able to use information about your monthly despatch volumes and typical parcel size and weight to negotiate best value prices.

Large Parcel

If your parcel is larger than 610mm x 460mm x 460mm in size, or weighs 20kg or more, Royal Mail categorises it as a Large Parcel and will pass you over to its Parcelforce service. Parcelforce is just one option, there are many other logistics companies for you to consider for best delivery service and price if you regularly send items in this bracket.

Ask The Experts

We hope the above advice gives you all the information you need to optimise your packaging to keep within Royal Mail size constraints and minimise your postal costs. eCommerce despatch operations are our speciality so if you have any unanswered questions or require further assistance then please get in touch – we’ll be more than happy to help.