Reviewed 30 September 2026 · quarterly cycle
Why is shipping more than I expected?
Almost always because billing is on chargeable weight rather than actual weight, and chargeable weight is the greater of the two. A light bulky parcel bills on air.
The evidence
The mechanism is the volumetric divisor. Chargeable weight is the greater of actual weight and volume divided by a divisor, and the divisor is published per service rather than per carrier. A box of 42 by 30 by 20 centimetres is about 25 litres; at a divisor of 6,000 that is 4.2 kilograms, and at 5,000 it is 5 kilograms. Neither figure has anything to do with what the parcel weighs.
The second reason is that the estimate you saw before dispatch was an estimate. Billed weight is measured at the warehouse rather than predicted, and the measured figure is what the line bills on. Where a parcel contains a filled jacket, a boxed pair of shoes or a structured bag, the measured figure routinely exceeds the estimate because the estimate was based on weight.
The third reason is surcharges, which are published but applied by period rather than stated at booking. Two identical parcels shipped a month apart can cost different amounts with no change to the goods or the destination. For a non-urgent shipment, moving out of a peak period is frequently a larger saving than switching lines.
When this does not apply
Where a line bills on actual weight rather than on the greater of the two, the volumetric calculation does not apply and the estimate usually holds. Checking the billing basis for the specific service before booking is what tells you which case you are in.