You can ship parcels as small as you want.
But smaller parcels are more expensive.
Naturally, the overhead service fee from the agent and the shipping line is calculated into the first weight increment. Usually, increments are 500g.
The first 500g cost $15, and each additional 500g cost $5.
- 500g parcel costs $15 ($30/kg)
- 4000g parcel costs $50 ($12.5/kg).
As you can see, shipping a bigger parcel is significantly more price effective. But there is a top limit, where you have to pay tolls and VAT.