Tonkilometers

Tonkilometers, also spelled tonne-kilometres or ton-kilometres, is a unit of freight transport activity. It represents the movement of one metric ton over a distance of one kilometer. The unit is independent of transport mode and is used to aggregate the volume of goods moved within a transportation system.

Calculation: For a shipment, ton-km equals cargo mass in tonnes multiplied by the distance traveled in kilometers. For multi-leg shipments, the ton-km value is the sum over each leg of (tonnes carried on that leg × distance of that leg). If the same cargo is moved across several legs, its ton-km contribution is added for each leg.

Applications: Ton-km is widely used in logistics and transport statistics to quantify total freight activity, compare intermodal performance, and assess productivity. It is also used in conjunction with energy and emissions data to express energy use or emissions per ton-km, enabling comparisons across modes and policy scenarios. National transport accounts and industry reports frequently present ton-km figures.

Advantages and limitations: The metric provides a simple, mode-agnostic measure of transport workload. It does not directly reflect energy consumption, emissions per unit, or profitability, since these depend on load factors, route distances, vehicle efficiency, and cargo characteristics. It should be interpreted alongside other indicators to assess performance or environmental impact.

Synonyms and related terms: The unit is equivalent to tonne-kilometre; in imperial units, a related measure is ton-mile. It is commonly used together with passenger-kilometres to describe overall transport activity.