Royal Mail parcel size checker & packing worksheet
Measure and weigh the complete package, including its wrapping. All three sides and the weight must fit the service's limits. The checker below finds supported rectangular formats; use the blank worksheet to compare packaging before buying postage.
Which rectangular format fits?
Enter the outside measurements after packing. Sides can be entered in any order. This checks physical format and quotes base postage for your selection.
Smallest matching format: Large letter
- Large letter: £2.70
- Small parcel: £3.95
- Medium parcel: £6.25
2–3 working day aim, including Saturday; not guaranteed. These are format choices for the selected service, not a comparison of every service or courier.
Base consumer prices; excludes signature, collection, Special Delivery, international and business services. Rectangles only; passing this check does not confirm contents or compensation eligibility. Official price guide for this selection.
How to measure a package
- Seal the package as it will be sent. Include padding, labels and any protective box.
- Measure the outside at its widest points, including bulges. Do not use the item's unpacked dimensions.
- Order the measurements longest, middle and shortest. For a flat envelope, the shortest measurement is thickness.
- Weigh the whole package. Check every limit; a light box can still be too large.
Illustrative diagram, not a scale drawing or printed sizing gauge. Use a ruler and scales.
Rectangular size limits at a glance
| Format | Maximum outside dimensions | Standard weight limit |
|---|---|---|
| Letter | 24 × 16.5 × 0.5 cm | 100 g |
| Large letter | 35.3 × 25 × 2.5 cm | 750 g |
| Small parcel | 45 × 35 × 16 cm | 2 kg |
| Medium parcel | 61 × 46 × 46 cm | 20 kg |
Large letters are limited to 750 g for 1st/2nd Class and Signed For. The July online and October price guides allow up to 1 kg for Tracked 24/48. Tracked does not have a letter format. Choose the correct service, date and channel in the checker.
Why a few millimetres matter
A 35 × 25 × 2.5 cm package weighing 700 g fits a standard large letter. If padding increases its thickness to 2.6 cm, it needs a parcel format. At 800 g it also exceeds the standard large-letter weight limit, although a Tracked large letter may fit under the dated guide's 1 kg allowance. The checker changes the format and quote together.
Do not squeeze unsafe packaging to fit a cheaper format. Compare the full cost, delivery aim and cover using the Royal Mail postage calculator.
Tubes, rolls and unusual shapes
The rectangular checker does not classify cylinders. The dated guides use a separate length-plus-twice-diameter rule for tubes and rolls, with additional limits. Record the length and outside diameter and check the official guide for your service before buying. International and Parcelforce rules differ.
For service limits and permitted contents, check Royal Mail's UK services and restricted items.
Sources and method
KnowTheCost is an independent publisher. This checker compares the three outside dimensions, sorted largest first, and packaged weight with the selected service's limits. It uses the same price data as our postage calculator. It is an estimate, not a carrier acceptance decision or guarantee.
Royal Mail July online guide · October online guide · October counter guide. Published periods are shown in the checker; confirm current terms at Royal Mail tariff updates.
Spot a mismatch? Email info@knowthecost.co.uk with the page, selected service and source reference. Avoid including personal details.