How can I use tonne-kilometres via the CO2 calculator? What are tonne-kilometres?

The tonne-kilometer is a unit of measurement used in the transport sector to quantify the volume of goods transported. It corresponds to the transport of one tonne of goods over a distance of one kilometer. 
It is used as a tracking indicator and can be used to calculate carbon emissions.

We recommend using grams of CO2 per parcel. This figure is more representative of carbon performance in the context of a single-package activity vs. the tonne-kilometer.