Shipping carbon footprint is the greenhouse gas emissions caused by moving freight, usually reported as CO2 or CO2e. It can be estimated from the fuel a vehicle burned, or from the weight carried, the distance travelled and an emission factor for the transport mode. Fuel data gives the more accurate answer when it is available.
How do you calculate freight CO2 emissions?
There are two practical methods. Use the fuel-based method when you know how much fuel a trip used, and the distance-based method when you only know weight, distance and mode.
- Fuel-based: CO2 = litres of fuel x emission factor of the fuel. Approximate tailpipe factors are 2.68 kg per litre of diesel and 2.31 kg per litre of gasoline.
- Distance-based: CO2 = tonnes x kilometres x emission factor per tonne-kilometre, divided by 1,000 when the factor is in grams and the result in kilograms.
A tonne-kilometre is one tonne of cargo moved one kilometre. It is the standard unit of transport work, and it lets you compare shipments of different sizes and distances. Intensity = grams of CO2 / tonne-km, where tonne-km = tonnes x kilometres. The shipping carbon footprint calculator applies the same two methods.
Worked example with fuel data
This is an illustrative trip: a truck burns 300 litres of diesel carrying 12 tonnes over 400 km.
- CO2 = 300 x 2.68 = 804 kg.
- Tonne-km = 12 x 400 = 4,800.
- Intensity = 804,000 g / 4,800 = about 168 g per tonne-km.
- CO2 per tonne of cargo = 804 / 12 = 67 kg.
The fuel figure captures real conditions: the truck, the load, the terrain and the driving. That is why it beats a generic average when the data exists.
Worked example with an emission factor
Suppose fuel data is missing, a carrier supplies a factor of 100 grams of CO2e per tonne-km for the lane, and the shipment is 10 tonnes over 600 km. The 100 is a made-up round number for illustration, not a published factor.
- Tonne-km = 10 x 600 = 6,000.
- CO2e = 6,000 x 100 g = 600,000 g.
- Convert to kilograms: 600,000 / 1,000 = 600 kg.
The method is simple, so the quality of the factor decides the quality of the answer. Take factors from your carrier or a published factor database for the correct mode, region and vehicle type, and record which source and year you used.
How do emissions differ by transport mode?
Emissions per tonne-kilometre differ a great deal by mode, so the mode usually matters more than any other input. The ranking below is qualitative, and actual factors vary with vehicle, load and route.
| Mode | Relative intensity per tonne-km | What drives the result |
|---|---|---|
| Ocean | Typically lowest | Ship size, speed, fuel type, load factor |
| Rail | Low | Electric or diesel traction, train length, load |
| Road | Moderate | Vehicle size, load factor, empty return trips, congestion |
| Air | Typically highest | Aircraft type, belly versus freighter, distance |
Within a mode, load factor is the biggest lever. A half-empty truck emits nearly as much as a full one but moves half the freight, so its intensity per tonne-km roughly doubles. Empty return trips have the same effect. Weight is not the only way to fill a vehicle, since light, bulky freight fills space before it reaches the weight limit. The freight density calculator helps with that side of the picture.
What do reporting standards say?
The simple formulas give an estimate. Corporate reporting needs a stated method and boundary. Under the GHG Protocol, transport bought from a carrier is typically reported as Scope 3 emissions, under upstream transportation and distribution for inbound and outbound freight you pay for, or downstream transportation for freight paid for by others. Emissions from vehicles you own and operate fall under Scope 1.
The GHG Protocol Scope 3 Standard describes fuel-based, distance-based and spend-based approaches and expects the more detailed data to be used where it is available. Other frameworks exist for logistics, including the GLEC Framework and ISO 14083, which set out how to quantify emissions across transport chains. If a customer or regulator asks for figures, ask which method they require before calculating, because the boundary decides the number.
Tailpipe versus well-to-wheel
The fuel factors in the formulas above cover tailpipe carbon dioxide only. They exclude the emissions from producing and delivering the fuel, and they exclude other greenhouse gases such as methane and nitrous oxide. A well-to-wheel figure includes the fuel supply chain and is higher. Choose one basis, state it in the report, and do not mix tailpipe and well-to-wheel numbers in the same comparison.
Common mistakes
- Mixing units: miles with kilometres, short tons with tonnes, litres with US gallons.
- Using a generic factor when carrier-specific data exists.
- Applying a one-way trip distance when the vehicle returned empty, or ignoring the empty leg when reporting a fuel-based trip.
- Averaging intensities across trips. Add the CO2 and tonne-km of each trip, then divide, so large shipments carry the right weight.
- Comparing two figures that use different boundaries, such as tailpipe CO2 against full CO2e.
- Treating the result as audited. Estimates need documented factors, a stated boundary and consistent methods before they support external claims.
How to use the result
Use intensity to compare lanes, carriers, vehicles and loading practices. Typical levers are higher load factors, fewer empty miles, a shift to rail or ocean where lead time allows, and consolidating shipments. Calculate before and after a change on the same basis, or the comparison tells you nothing. Further reading on logistics decisions is on the logistics and transportation hub, and wider reduction topics are covered under sustainable supply chain.
Analytics helps mainly with data capture. Telematics and transport management systems can feed fuel use, distance and load weights into the calculation automatically, which reduces manual entry. The factors, the boundary and the choice of method still need a person to decide and document them.
Common questions
What is a tonne-kilometre?
A tonne-kilometre is one tonne of cargo moved one kilometre. It measures transport work and lets you compare emissions across loads and distances. Multiply cargo weight in tonnes by distance in kilometres, then divide total emissions by that figure to get intensity.
Which method should I use?
Use the fuel-based method when you have fuel data for the trip, since it reflects real conditions. Use distance and an emission factor when fuel data is unavailable. Spend-based estimates are a last resort because they are the least precise.
Why is my intensity different from published factors?
Published factors are averages across many vehicles and trips. Your result depends on load factor, vehicle type, terrain, empty return trips and driving style. A gap is normal, and a large one is worth investigating because it often points to low utilization.
Is CO2 the same as CO2e?
No. CO2 counts carbon dioxide only, while CO2e converts other greenhouse gases such as methane and nitrous oxide into carbon dioxide equivalents. Reporting standards usually ask for CO2e, so check which one your factor and your report use.
Sources and further reading
- Corporate Value Chain (Scope 3) Standard (GHG Protocol)
- Transport Canada (Transport Canada)
- MIT Center for Transportation and Logistics (MIT CTL)