Shipping Emissions Calculator

This calculator estimates the carbon footprint of moving freight and lets you compare transport modes directly. You enter the cargo weight and distance, pick a mode, and it multiplies through DEFRA tonne-kilometre factors to give the CO2e, alongside a table of all four modes so the cleanest choice is obvious.

How it works

Freight emissions scale with how much you move and how far, multiplied by the mode’s emission factor per tonne-kilometre:

tonne_km = weight_tonnes × distance_km
co2e_kg  = tonne_km × factor_per_tonne_km

Typical DEFRA factors are about 0.012 kg CO2e per tonne-km for a large container ship, 0.027 for rail, 0.11 for an HGV, and 0.6 for long-haul airfreight — a roughly fiftyfold range that makes mode the single biggest lever in freight carbon.

Why mode choice dominates freight carbon

The gap between airfreight and sea freight is so large that almost nothing else in a logistics operation matters as much as keeping cargo off aircraft. A 5-tonne shipment moved 8,000 km by sea produces around 480 kg CO2e. The same shipment by air produces roughly 24 tonnes — fifty times more. That difference dwarfs any packaging optimisation, warehouse energy saving, or last-mile efficiency gain.

Rail sits between sea and road for most corridors: electrified rail is substantially cleaner than diesel HGV, and even diesel rail is generally less carbon-intensive per tonne-km than road. Where rail connections exist for a route, they are usually the second-cleanest option after deep-sea shipping.

Understanding the factors

The DEFRA conversion factors used here are published annually in the UK government’s greenhouse gas reporting guidance. They are averages across a mode’s typical operating conditions — vessel size, load factors, fuel type — and differ from what any single specific shipment produces. Key points:

• The container-ship factor assumes a large ocean vessel at typical load. A smaller feeder vessel on a short-sea route has a higher per-tonne-km factor.
• The HGV factor assumes an average articulated truck at average load. An empty or part-loaded truck has a much worse effective factor because the denominator (cargo tonnes) is smaller.
• The airfreight factor covers the combustion emissions of the flight. Including the warming effect of contrails and high-altitude NOx (the Radiative Forcing Index) would raise the airfreight number further, but that uplift is not yet standardised in DEFRA reporting, so this tool uses the fuel combustion factor only.

Scope 3 reporting context

In GHG Protocol Scope 3 reporting, freight emissions fall under:

• Category 4 — Upstream transportation and distribution (goods moving toward you)
• Category 9 — Downstream transportation and distribution (goods moving to customers)

Activity-based tonne-km calculation (weight × distance × factor) is the recommended primary method when you have shipment data. Spend-based estimation is only used when activity data is unavailable and gives lower accuracy.

For procurement teams, this tool supports supplier engagement under Category 4: you can compare the emissions impact of switching a supplier whose goods travel by air to one whose goods travel by sea, turning the decision into a concrete carbon number.

Example scenarios

For illustration, consider these example calculations using the DEFRA approximate factors:

These are illustrative estimates using approximate factors. Actual figures depend on vessel, load factor, and specific routing.