HS code
The customs number that decides the duty on every international parcel.
What it is
The Harmonized System code is the six-digit product classification customs authorities share worldwide. Countries extend it for their own tariffs; the US and the UK use ten digits. It goes on the customs declaration of every parcel that crosses a border and sets the duty rate.
Why it costs you money
A missing code holds the parcel while the carrier asks for one; a wrong code means the wrong duty, which either overcharges your customer or lands back on you as a correction. If you quote duties at checkout, every quote is only as good as the code behind it.
How to check it yourself
WooCommerce has no HS code field out of the box, so keep the code in your label tool or a custom product field. Look codes up in the destination's official tariff search, such as the US HTS or the UK Trade Tariff, starting with your best-selling products.