The limit a repeat size has to respect
For senders of fewer than 1,000 parcels a year, our changes page records one small-parcel maximum since October 2014. The outside of the carton is 450 x 350 x 160 mm. The older pair of limits, 450 x 350 x 80 mm and 350 x 250 x 160 mm, were merged into that.
A Packaging Wholesale size that is a few millimetres over that outside measurement is a standard parcel. The page says a small parcel costs less than a standard one.
Rolls on the same account
A roll or cylinder can still be a small parcel up to 450 mm long and 80 mm in diameter. That exception is not the square-box maximum.
White postal cartons in stock are described as qualifying for the small parcel rate. The trade rate does not change the millimetres.