Hi,

It is at

https://sellercentral.amazon.co.uk/gp/help/help.html?itemID=G200141510&language=en_GB

Box weight and dimensions

• Boxes containing multiple standard-size items must not exceed 63.5 cm on any side. A box may exceed the 63.5 cm if it contains oversize units that measure longer than 63.5 cm. Boxes that are excessively large relative to the oversize units may be subject to restriction of shipping privileges, additional fees, or refusal at a fulfilment centre.
• If you are using an Amazon-partnered carrier, make sure that you accurately weigh and measure boxes and pallets to ensure that the correct values are supplied for every shipment.
• Boxes must not exceed the standard weight limit of 23 kg, unless they contain one single oversized item that exceeds 23 kg.
  • Boxes weighing between 15 kg - 23 kg must contain “Heavy Package” label viewable from the top and sides of each heavy-weight container (5 labels in total).
  • For a single oversized item that exceeds 15 kg, attach a “Heavy Package” label from the top and sides of each heavy-weight container (5 labels in total).