If the cost of shipping hay has ever surprised you, it's not a mistake or overcharging: hay is simply the product that fares worst under the way Correos —and any carrier— calculates a shipment's price.
What volumetric weight is
Almost no carrier charges by the real weight on the scale. They charge by the greater of two values: the real weight, or the "volumetric weight", calculated from the size of the box. With Correos, the formula —set out in our own contract— is:
length × width × height, in centimetres, divided by 6,000
The result is the kilos you get billed for, whatever the scale says. It's not a special rate for us: it applies the same way to Paq Estándar, Paq Premium and Paq Today.
Why hay is the worst case
Hay is bulky and light: a lot of volume, little real weight. That pushes the volumetric weight far above the real one, so it's always the volumetric weight that gets billed. It's the same reason it costs more to ship a duvet than an equally large box full of metal parts: you don't pay for the weight, you pay for the space it takes up in the van.
Our shipments, with real numbers
Correos measures the parcel and calculates its volume: these are the brackets it has actually billed us, according to our own invoices.
| Format | Volumetric weight | Bracket billed by Correos |
|---|---|---|
| 3 kg | 8.0 kg | 5 to 10 kg |
| 5 kg | 13.3 kg | 10 to 15 kg |
| 10 kg | 16.7 kg | 10 to 15 kg |
The clearest case is the 3 kg format: it weighs 3 kg on the scale, but because of the box's real size Correos bills it in the 5 to 10 kg tier — up to more than triple what it actually weighs.
Why it can't be avoided
Compressing the hay further reduces volume, but it has a physical limit: the bale itself. And splitting it into smaller boxes doesn't help either, because the volumetric weight is calculated per parcel, not by the total kilos shipped.
