Royal Mail Sizes: Mailing Bags vs Padded Envelopes
Key Takeaway
Royal Mail prices by size as well as weight. How grey mailing bags and padded envelopes help keep orders in the cheaper Large Letter size.
Royal Mail charges by the size of a parcel as well as its weight. Posting a small, light item in a box can push it into a more expensive size. Flat mailers help keep it in the cheaper one.
The Royal Mail sizes that matter
| Format | Maximum size | Maximum weight |
|---|---|---|
| Large Letter | 35.3 x 25 x 2.5 cm | 750 g |
| Small Parcel | 45 x 35 x 16 cm | 2 kg |
Source: Royal Mail, How to send small parcels. The key limit is the 2.5 cm thickness: go over it and the item becomes a Small Parcel.
Grey mailing bags
Grey mailing bags are thin polythene mailers with a self-seal strip. They add almost nothing to the size or weight of what is inside. They have no padding.
- Best for: clothing, soft goods, items already in their own packaging.
Padded mailing envelopes
Padded mailing envelopes are paper envelopes lined with bubble cushioning. They protect small items that could scratch or dent, while staying thin enough for many Large Letter orders.
- Best for: jewellery, phone cases, cosmetics, small books, crafts.
Jiffy padded bags
Jiffy padded bags use paper padding instead of bubbles. They are thicker and tougher, so they suit heavier or sharper small items.
- Best for: metal parts, spares, hardback books.
Quick decision guide
| Your item | Use |
|---|---|
| Soft and flat (clothing, textiles) | Grey mailing bag |
| Small and delicate, needs to stay under 2.5 cm | Padded mailing envelope |
| Small, heavy or sharp-edged | Jiffy padded bag |
Measure before you choose
Pack one real order, then measure its thickness. If it is close to 2.5 cm, a thinner mailer can be the difference between Large Letter and Small Parcel prices.
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