How to use the parcel size checker

Measure the parcel after it has been packed, not the item before packaging. Use the longest side as length, the next side as width, and the smallest side as height or thickness. Enter the packed weight in kilograms.

The calculator sorts the dimensions for you, so it does not matter which way round you hold the parcel. The result shows the first size band that the parcel is likely to fit.

What the result means

The checker uses common planning bands for letter, large letter, small parcel and medium parcel. It is useful for spotting when a parcel is too thick for large letter, too heavy for small parcel, or likely to need a larger service.

It does not buy postage, quote live prices or replace the courier's final rules. Always check the exact service before posting, especially for tubes, international parcels, high-value items, batteries or restricted goods.

Size bands used in this checker

The letter check is for very flat items. The large letter check is for thin parcels such as documents, slim books, small clothing items in a flat mailer, or other items that stay within a low thickness limit. The small parcel check is for compact boxed or bagged items. The medium parcel check is for bulkier parcels that are still within the larger planning band used here.

If your item is soft, squashy or uneven, measure it at the thickest point after packing. If it only fits when pressed down, treat it as the next size up. Sorting machines and counter checks normally care about the packed parcel, not the neatest way you can hold it.

Seller workflow

Use this checker first to understand the likely size band. Then use the postage comparison calculator to compare current label prices, compensation cover and tracking. After buying a label, the PDF Label Mover can help place the label onto a spare A4 label sheet position.

For marketplace selling, also check the final fee and profit before accepting a low offer. Postage size, promoted listing rate, packaging cost and seller fees can change whether the sale is worthwhile.

Common mistakes

Do not measure the product box before adding an outer bag, padding or tape. A parcel that is just under a limit can move into the next band if the corners bulge or the label sheet is folded around the item.

Weigh the parcel with the label, packaging and any invoice or note included. If the parcel is close to a limit, leave a margin rather than relying on the exact number shown here.

Example checks

A phone case in a slim padded envelope might look like a large letter until the padding and corners are measured. A folded jumper may fit a small parcel bag, but the packed thickness can be the deciding number. A boxed pair of shoes may be comfortably within a medium parcel size but still needs checking against the courier's weight and compensation rules.

When in doubt, compare the next size up before buying the label. Paying slightly more for the right size band is usually better than having the parcel delayed, returned, surcharged or refused.