Measure the package that will actually be handed over
Begin with the final packaging rather than the product’s catalogue dimensions. Royal Mail’s heavy-item guide asks senders to weigh the parcel including its packaging and measure the box’s length, width and depth. A supplier’s item weight can omit the carton, cushioning, inserts and tape. Those materials are part of the packed shipment, even when they seem small compared with the goods.
Our recommended measurement record uses the sealed package’s maximum external dimensions, including bulges or protruding parts, and its actual gross weight. Keep the units beside every value. Measure again after adding protective materials or changing the carton. Record which parcel was measured so customer service and the booking team do not accidentally reuse figures for an earlier version of the packaging.
Use the four 1st Class formats as a defined reference
The reviewed Royal Mail 1st Class page lists the following maximum dimensions and weights. These provide the reference used by our rectangular format checker. All the relevant dimensions and the gross weight must fit; a parcel does not qualify merely because its longest side is within the limit.
This is a UK 1st Class format reference. It does not establish that every Royal Mail product accepts the same weights, that a particular account can book it, or that its contents are permitted. Compare the result with the exact service and purchasing channel before buying postage.
- Letter: 24 × 16.5 × 0.5 cm, up to 100 g.
- Large Letter: 35.3 × 25 × 2.5 cm, up to 750 g.
- Small Parcel: 45 × 35 × 16 cm, up to 2 kg.
- Medium Parcel: 61 × 46 × 46 cm, up to 20 kg.
Check thickness and weight as independent constraints
Consider a sealed pack measuring 35 × 24 × 3 cm and weighing 250 g. It is light enough for the Large Letter weight reference, but its 3 cm thickness exceeds the 2.5 cm limit. Conversely, a 30 × 20 × 10 cm box weighing 2.1 kg fits the Small Parcel dimensions but exceeds its 2 kg weight reference. Each would need review against another format and the selected product.
Our checker can rotate the three dimensions of a rectangular item when comparing them with the reference limits. Rotation changes which side is called length, width or depth; it does not make the package smaller. Do not round a measurement down to obtain a preferred result. If your measurement is uncertain at a boundary, recheck the finished parcel rather than treating the tool as a carrier acceptance decision.
Read the product and purchase channel after the format check
Royal Mail’s consumer Tracked 24 page illustrates why a format reference needs a stated scope. Its reviewed table allows a Large Letter weighing up to 750 g when postage is purchased at a Post Office, and up to 1 kg for an online purchase. The dimensions remain 35.3 × 25 × 2.5 cm. A 900 g flat item therefore needs a product-and-channel check instead of a universal assertion that every Large Letter must stop at 750 g.
The reviewed consumer Tracked 24 parcel limit is 20 kg, while the business Tracked 24 and 48 page advertises parcels up to 30 kg within 61 × 46 × 46 cm. That business specification depends on the applicable account service. Confirm the contracted product, options, presentation and posting arrangements with the booking party. Neither the reference checker nor a general product page establishes your account’s eligibility.
Keep tubes and irregular shapes outside a rectangular result
The checker is designed for rectangular packages with three outer dimensions. Tubes, rolls and irregular shapes need their own review. Royal Mail’s product pages list tubes and rolls separately, including rules involving diameter. Entering a tube’s bounding box into a rectangular tool cannot establish that it satisfies those separate rules or is permitted under the chosen service.
Likewise, a size match does not inspect packaging strength, restricted contents, addressing, compensation conditions or the drop-off facility. Preserve a readable label and check the final service instructions before release. If protective packing changes the format, update the order’s measurement and booking records together. Do not remove needed protection simply to reproduce an earlier, smaller measurement.
Separate the UK format from the China–UK transport quotation
For Jeton Express consolidation, measure each final parcel after Guangzhou packing and keep it linked to the supplier orders and international batch. The Royal Mail format describes the proposed UK parcel stage. It does not calculate the charge for international air transport, clearance, warehouse work or the complete China–UK journey. Ask the provider to identify the measurement and charging rules for each quoted stage.
Our general measurement guide can help organise actual weight, volumetric weight and cubic volume for that discussion. Confirm the chosen service’s volumetric divisor, assessment by parcel or shipment, rounding and minimum charge rather than borrowing one formula from another route. If stock goes to Edinburgh before later customer dispatch, keep inbound transport measurements separate from the parcels packed for those customer orders. Retain the final measurement date, parcel count and approved booking with the dispatch record.
Official references
References reviewed on 2026-10-07. Check current product and help terms before booking or making a claim.