When you’re sending mail using a franking machine, understanding Royal Mail’s size categories is key to avoiding overpaying – or worse, having your mail rejected. Two of the most commonly confused categories are Large Letter and Small Parcel. In this guide, we’ll break down the differences, explain when to use each, and show how to easily measure your mail using the Royal Mail Size Guide.
Every millimetre counts. Sending something as a Small Parcel when it qualifies as a Large Letter could cost your business up to 50% more in postage. With Royal Mail, pricing is based on format and weight, and the line between categories can be surprisingly slim.
A Large Letter is bigger than a standard letter but still flat enough to fit through a letterbox. According to Royal Mail’s guidelines, to qualify as a Large Letter, your mail must:
✅ Tip: If your item is uniform and doesn’t bulge beyond 2.5cm thick, it likely qualifies as a Large Letter.
If your item is bulkier or exceeds the dimensions above, it falls into the Small Parcel category. These parcels can be:
The best way to check is with a Royal Mail Size Guide, like the one included in our Mailcoms Starter Packs or the one we send out to you with your first online order with us. Simply try sliding your item through the slots prior to franking your mail item.
Franking machines make postage more cost-effective – but only when used correctly. Accidentally franking at the wrong rate can lead to:
Using the right size category helps you stay accurate, efficient, and compliant.
Sending your mail at the correct size and format isn’t just about compliance – it’s about saving money and avoiding hassle. With a franked item, you already benefit from Mailmark discounts – now make sure you’re not overspending due to misclassification.
At Mailcoms, we offer a range of franking machines. If you are interested in getting a franking machine or wish to upgrade to a Mailmark franking machine with even lower prices available, then please view our franking machine page here or call us today on 01543 572 776.
We are a Royal Mail Authorised Independent Inspector & Maintainer of Franking Machines with over 20,000 customers nationwide and we can supply you with our very own range of models.