Small Parcel Size for Royal Mail UK: Exact Dimensions and Weight Limits
What size is a small parcel for Royal Mail?
A Royal Mail small parcel must fit within 450mm x 350mm x 160mm and weigh no more than 2kg. Those are the maximum measurements. If your package exceeds any one of those three dimensions, or goes over the 2kg weight limit, it moves into the large parcel category.
Royal Mail publishes its full size and weight guide on its website. You can check the current limits directly on the Royal Mail size and weight guide page.
How does a small parcel compare to other Royal Mail formats?
Royal Mail uses four main size formats, and the price you pay depends on which one your item falls into.
| Format | Max length | Max width | Max depth | Max weight |
|---|---|---|---|---|
| Letter | 240mm | 165mm | 5mm | 100g |
| Large letter | 353mm | 250mm | 25mm | 750g |
| Small parcel | 450mm | 350mm | 160mm | 2kg |
| Medium parcel | 610mm | 460mm | 460mm | 20kg |
These figures are correct at the time of writing. Always check the Royal Mail website before sending, as limits and prices do change.
Why do the dimensions matter so much?
Royal Mail sorts parcels using automated machinery, and the size thresholds reflect what fits through that equipment. Even a small overhang on one side can push your parcel into a higher price band. It is worth measuring your packed item carefully rather than estimating by eye.
The depth limit of 160mm is often the one that catches people out. A box that looks compact can easily creep past that if you have added bubble wrap or internal padding.
Is there a minimum size for a small parcel?
Yes. Royal Mail requires any item classed as a parcel to measure at least 100mm x 70mm. Items smaller than this cannot be processed through standard postal services. The minimum depth for a parcel is 10mm.
What packaging works well for small parcels?
The goal is to protect your item while keeping the overall dimensions under the limits. A few practical points:
- Choose a box that is a snug fit for your product. Too much empty space means you need more void fill, which adds depth and weight.
- Measure the outside of the finished, packed box. That is what Royal Mail measures, not the internal dimensions.
- Use enough padding to prevent movement inside, but keep it proportionate. A single layer of bubble wrap adds roughly 10mm to 15mm per side.
- Check the total weight after packing. Packaging materials contribute to the final figure, and 2kg is the hard ceiling for this format.
Getting the size right before you buy your packaging avoids the need to repack or pay a surcharge at the post office.
What happens if your parcel is slightly over the size limit?
Royal Mail will reclassify it as a medium parcel. That means a higher postage cost. If you have already paid for a small parcel label and the item is found to be over size, Royal Mail may apply a surcharge or return the item. It is much easier to check dimensions before you seal the box.
How do you measure a parcel correctly?
Use a tape measure or ruler along the outside of the sealed package. Measure the longest edge for length, the next longest for width, and the shortest for depth. Include any protrusions, handles, or labels that add to the overall size. If the box has a slight bow in the side from packing, measure at the widest point.