How to use the Royal Mail size guide ruler correctly

The Royal Mail size guide ruler is a slotted plastic template that tells you which postage category your item falls into. To use it, slide your letter or parcel through the slots from smallest to largest – the first slot it does not fit through is its size category, which tells you the correct postage to frank.

What the ruler measures

The template has slots based on Royal Mail’s official dimensions for:

• Letter
• Large Letter
• Small Parcel

Picking the right category before you frank means you pay the correct rate and avoid items being rejected or surcharged.

Step by step

1. Try the item in the Letter slot first. If it passes through easily, it’s a Letter (subject to weight).
2. If it doesn’t fit, try the Large Letter slot. If it passes, it’s a Large Letter.
3. If it’s too big for Large Letter, it’s a Small Parcel or larger – frank it accordingly.
4. Always check weight too: size and weight together decide the format and price.

Why it matters

Getting the format wrong is one of the most common causes of Royal Mail surcharges. A few seconds with the ruler protects you from underpayment and from items being returned. At Mailcoms we include a Royal Mail size guide ruler with every franking machine starter pack and every first-time online order.

Need a replacement ruler or franking supplies? Browse our franking supplies.

FAQs

What are the three size slots? Letter, Large Letter and Small Parcel, based on Royal Mail’s official dimensions.

Does size alone decide the price? No – size and weight together decide the format and the postage you pay.

Where do I get a size guide ruler? Mailcoms includes one with every franking machine starter pack and every first-time online order.