Tonne-Kilometre (tkm): the "currency" of transport

The tonne-kilometre (tkm) is the fundamental unit of measurement in logistics and the foundation of every GLEC calculation. Understanding it is the first step to correctly interpreting your emissions data.

What is the tkm?

Imagine you want to measure “how much work” a truck does. Knowing how many kilometres it travels is not enough, and neither is knowing how much weight it carries. You need to combine both.

Formula:

tkm = (weight in kg / 1000) × distance in km

Practical example

Situation	Weight	Distance	tkm
Truck A	10 tonnes	100 km	1,000 tkm
Truck B	5 tonnes	200 km	1,000 tkm
Truck C	20 tonnes	50 km	1,000 tkm

All three trucks perform the same “transport work” (1,000 tkm), even though they do it differently.

Why is it useful?

CO₂ emissions depend on that “work”. A truck carrying more weight or travelling further emits more. The tkm lets you compare apples with apples.

The logic behind this is that emissions depend on the type and quantity of fuel used, and the quantity of fuel depends on the tkm consumed.

The tkm in your GLEC report

In your GLEC report you will see tkm as an activity indicator: the more tkm, the more logistics activity and, potentially, the more emissions. But the intensity (gCO₂e/tkm) lets you compare the efficiency of different routes, vehicles, or periods.

Indicator	What it measures
Total tkm	The volume of logistics activity
gCO₂e/tkm	Emission efficiency per unit of activity
Total kg CO₂e	The absolute impact for the period

Reducing intensity (gCO₂e/tkm) — without necessarily reducing tkm — is the logistics efficiency goal in plans such as Lean & Green and SBTi.