Shipping tiers for WooCommerce

Hello,

I am trying to set up WooCommerce (or another shopping cart) to ship items in “tiers” (not sure if this is the right word even). The different levels mean that to ship one or three items costs the same. The levels look like this:

1-3 items – $6
4-9 items – $13
10-12 items – $17

Does anyone know what this shipping method would even be called? I’ve looked at the Woo documentation, and I don’t see how I could make flat rate shipping or table rate shipping do this.

Thanks in advance for you help,

Damian