Royal Mail Parcel Sizes: Small, Medium & Large (UK)

Royal Mail prices UK post by size band and weight, so knowing the limits before you pack saves money and stops parcels being surcharged or returned. This guide lists every UK size band, explains how to measure a parcel, and shows which of our boxes and mailing bags fit each one.

Royal Mail 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.

Small Parcel

• Maximum size: 45 cm × 35 cm
• Maximum depth: 16 cm
• Maximum weight: 2 kg
• Typical use: shoes, portable speakers, mobile phones and other small items.

Medium Parcel

• Maximum size: 61 cm × 46 cm
• Maximum depth: 46 cm
• Maximum weight: 20 kg
• Typical use: gifts, shoes, and heavy or bulky items.

Anything bigger or heavier than a Medium Parcel goes by Parcelforce Worldwide: up to 1.5 m long, 3 m length and girth combined, and 30 kg.

Royal Mail UK size and weight limits

*Large Letters bought online with UK Tracked have a 1 kg limit. Special Delivery Guaranteed has its own weight limits: 20 kg by 1pm and 2 kg by 9am. Limits taken from Royal Mail's size and weight guide (checked 28 September 2026). Royal Mail can change them, so check the guide before a big mail-out.

Sending something flat? Letters and Large Letters are cheaper than parcels: see our Royal Mail large letter size guide.

Royal Mail small parcel size

A Small Parcel must not be more than 45 cm long, 35 cm wide and 16 cm deep, and must weigh 2 kg or less. All three measurements must fit at the same time: a parcel 40 cm long but 18 cm deep is a Medium Parcel, even though it is short.

These of our boxes fit the Small Parcel band with at least 10 mm to spare on every side. The spare allows for the board thickness, because the outside of a box is a little bigger than its internal size:

Flat mailing bags up to 330 × 435 mm (grey mailing bags), Jiffy bags up to size 5 (245 × 381 mm), padded envelopes up to 240 × 335 mm and bubble bags up to 305 × 425 mm are within the Small Parcel length and width when flat. A filled bag gets shorter and narrower as it gets thicker, so measure the packed parcel, and keep it under 16 cm deep.

Royal Mail medium parcel size

A Medium Parcel can be up to 61 × 46 × 46 cm and 20 kg. Most of our single wall boxes and double wall boxes fit this band, from 152 × 152 × 152 mm cubes up to 457 × 305 × 305 mm (18 × 12 × 12 in) and 406 × 406 × 406 mm (16 × 16 × 16 in). For heavy Medium Parcels, choose double wall boxes: they resist crushing much better in transit.

Is there a Royal Mail large parcel size?

Not for UK post. Royal Mail's largest UK format is the Medium Parcel. Anything bigger or heavier goes through Parcelforce Worldwide (Royal Mail's parcel business): up to 1.5 m long and 3 m length and girth combined, and up to 30 kg. Oversized items can go up to 2.5 m long and 4 m length and girth on Parcelforce's large-parcel services.

Girth is the distance around the parcel at its thickest point: twice the width plus twice the depth.

How to measure a parcel

• Measure the outside of the packed parcel, not the box's internal size, and include any bulges from overfilling.
• Length is the longest side, width the next longest, and depth the shortest.
• Weigh it with the packaging: box, void fill and tape all count towards the limit.
• Check all three sizes and the weight. Going over any one of them moves the parcel into the next band.

Tips for staying in the cheaper band

• Choose the smallest box that still leaves room for protection. Empty space adds size, not safety.
• For soft goods such as clothing, a mailing bag is lighter and slimmer than a box.
• Seal boxes with an H pattern of packing tape so they arrive closed without bulging.
• If a parcel is close to the Small Parcel depth, a lower box such as 305 × 229 × 102 mm (12 × 9 × 4 in) keeps it in the band.

Frequently asked questions

What is the maximum size for a Royal Mail small parcel?

45 cm long, 35 cm wide and 16 cm deep, weighing up to 2 kg.

What is the maximum size for a Royal Mail medium parcel?

61 cm long, 46 cm wide and 46 cm deep, weighing up to 20 kg.

What is the largest parcel Royal Mail will take?

For UK post, the Medium Parcel (61 × 46 × 46 cm, 20 kg). Larger parcels go by Parcelforce, up to 1.5 m long and 30 kg.

What box fits a Royal Mail small parcel?

Any box whose outside size is within 45 × 35 × 16 cm. From our range, the 305 × 229 × 102 mm (12 × 9 × 4 in) and 250 × 250 × 135 mm (10 × 10 × 5 in) single wall boxes are popular choices. The full list is in the table above.

See every size, pack quantity and trade price on our single wall boxes and mailing bags pages.