Royal Mail Large Letter Size: Dimensions & Weight Limits

A Large Letter costs less to post than a parcel, so fitting an item into Large Letter size is one of the easiest ways to cut postage. The catch is that Royal Mail checks length, width, thickness and weight, and going over any one of them makes it a Small Parcel. Here are the exact limits, what fits, and which mailing bags and envelopes keep you within them.

Royal Mail letter size bands at a glance

Letter

• Maximum size: 24 cm × 16.5 cm
• Maximum thickness: 0.5 cm
• Maximum weight: 100 g
• Typical use: cards, personal letters, postcards and bills.

Large Letter

• Maximum size: 35.3 cm × 25 cm
• Maximum thickness: 2.5 cm
• Maximum weight: 750 g (1 kg with UK Tracked bought online)
• Typical use: A4 documents, certificates, magazines, and CDs or DVDs in their cases.

Anything larger, thicker or heavier than a Large Letter is a Small Parcel (up to 45 × 35 × 16 cm and 2 kg).

Royal Mail letter and large letter sizes

*Large Letters bought online with UK Tracked have a 1 kg weight limit. Limits taken from Royal Mail's size and weight guide (checked 28 September 2026). Royal Mail can change them, so check before a big mail-out.

What fits in a Large Letter

Royal Mail's own examples of Large Letters are A4 documents, certificates, magazines, and CDs or DVDs in their cases. An A4 sheet (210 × 297 mm) fits flat with room to spare. Thin clothing items, such as a folded T-shirt in a slim mailing bag, can also fit if the packed item stays under 2.5 cm thick and 750 g.

The thickness limit is the one that catches people out

Most items that fail Large Letter do so on thickness, not length. 2.5 cm is about the thickness of a thick paperback. A bulging bag, a boxed item, or a stack of paper that is too thick all push the item up to Small Parcel.

• Measure at the thickest point, including the flap, any bubble lining and anything that bulges.
• Keep it flat: a slim mailing bag adds almost no thickness, while a padded bag adds some.
• Weigh it with the packaging: the bag or envelope counts towards the 750 g limit.

Mailing bags and envelopes that fit Large Letter size

These of our products are within the Large Letter length and width when flat. Padded envelope and Jiffy bag sizes are internal sizes, and the outer edge is a little bigger, so the sizes near the limit are marked "measure first":

Whatever you use, the filled item must still be no more than 2.5 cm thick and 750 g. For items that are too thick or heavy, see Royal Mail parcel sizes for the Small and Medium Parcel limits.

Letter vs Large Letter vs Small Parcel

• Letter: cards and folded letters up to 24 × 16.5 × 0.5 cm and 100 g.
• Large Letter: flat items up to 35.3 × 25 × 2.5 cm and 750 g.
• Small Parcel: anything larger, up to 45 × 35 × 16 cm and 2 kg.

Frequently asked questions

What is the Royal Mail large letter size?

Up to 35.3 cm long, 25 cm wide and 2.5 cm thick, weighing up to 750 g.

What is the maximum thickness for a large letter?

2.5 cm, measured at the thickest point of the packed item.

What is the Royal Mail letter size?

Up to 24 cm long, 16.5 cm wide and 0.5 cm thick, weighing up to 100 g.

Can I send A4 documents as a large letter?

Yes. A4 (210 × 297 mm) fits within the Large Letter length and width, as long as the packed item is no more than 2.5 cm thick and 750 g.

See all sizes and trade prices for grey mailing bags, padded envelopes and bubble bags.