Freight and shipping carbon calculator (road, sea, air, rail)

How this calculation works

Freight emissions follow one formula, applied once per transport mode:

Emissions (kgCO₂e) = tonne-kilometres × mode emission factor (kgCO₂e/tonne-km)

A tonne-kilometre (tonne-km) is the freight industry's unit of work: one tonne of goods moved one kilometre. To compute it, multiply shipment weight in tonnes by distance in kilometres. A 2-tonne pallet consignment trucked 500 km is 2 × 500 = 1,000 tonne-km. An 18-tonne container shipped 8,000 km by sea is 144,000 tonne-km. If you know the weight and the distance — both of which sit on your freight invoice or air waybill — you know the tonne-km. No fuel data from the carrier is required.

That matters because, for most organizations, freight is moved by someone else. Under the GHG Protocol, transport you pay a third party to perform sits in Scope 3, category 4 — upstream transportation and distribution, and the tonne-km approach (the Protocol calls it the distance-based method) is the standard way to estimate it when you don't have carrier-specific fuel data. Trucks you own and fuel yourself are a different animal: those litres are Scope 1 and belong in the fleet fuel calculator instead.

Enter your tonne-km per mode above — monthly or annual, as long as you're consistent — and the calculator applies the matching factor to each mode, then sums them.

The factors — and the 50× gap

This calculator uses the UK Government's 2025 greenhouse gas conversion factors (DEFRA/DESNZ) for freighting goods, published under the Open Government Licence v3.0 and widely used internationally as default freight factors where no local set exists:

| Mode | Factor (kgCO₂e/tonne-km) | | --- | --- | | Sea freight | 0.0116 | | Rail freight | 0.0281 | | Road freight | 0.1153 | | Air freight | 0.6022 |

Read the table bottom-up and the story tells itself. Moving one tonne of cargo one kilometre by air emits 0.6022 kgCO₂e — more than fifty times the 0.0116 of sea freight. Road sits in the middle at 0.1153, and rail is roughly four times cleaner than road at 0.0281. No packaging change, efficiency programme, or carrier negotiation moves a freight footprint the way changing the mode does. The exact factor, source year, and licence used for your calculation are printed under the result, so the provenance travels with the number.

A worked example

Say you ship 2 tonnes of components 10,000 km from an overseas supplier to your warehouse. That is 20,000 tonne-km either way — the mode decides everything else.

By sea:

20,000 tonne-km × 0.0116 kgCO₂e/tonne-km = 232 kgCO₂e ≈ 0.23 tCO₂e

By air:

20,000 tonne-km × 0.6022 kgCO₂e/tonne-km = 12,044 kgCO₂e ≈ 12.0 tCO₂e

Same cargo, same distance, and the air option carries an extra ~11.8 tCO₂e — more than a 20-person office typically emits from a full year of electricity. Meanwhile the trucking legs at each end barely register: 2 tonnes × 60 km from port to warehouse is 120 tonne-km × 0.1153 = about 14 kgCO₂e, a rounding error next to the air-versus-sea decision.

This is why mode shift is the biggest lever in category 4. Reserving air for genuinely urgent goods and moving everything else by sea can cut a freight footprint by an order of magnitude; shifting long-haul road legs to rail cuts those legs by roughly three-quarters. Consolidating shipments so fewer of them fly, and forecasting demand earlier so fewer orders become "urgent" in the first place, both pull in the same direction — and both show up immediately when you recalculate the tonne-km split.

A second worked example: restocking under time pressure

A small fashion importer typically brings in stock by sea — 6 tonnes a quarter over 9,000 km from a regional supplier, or 54,000 tonne-km. Sea freight for that volume comes to 54,000 × 0.0116 = 626.4 kgCO₂e for the quarter, a modest number for the size of the business.

Then a bestselling line sells out mid-season and the importer air-freights a 200 kg restock over the same 9,000 km to catch the remaining weeks of demand: 0.2 tonnes × 9,000 km = 1,800 tonne-km, and 1,800 × 0.6022 = 1,083.96 kgCO₂e — more than the entire quarter's planned sea freight, from a shipment weighing barely 3% as much. This is the pattern that shows up repeatedly in apparel and other seasonal-demand categories: unplanned air restocks, individually small in volume, can dominate a freight footprint precisely because they are reactive rather than forecast, and forecasting accuracy is therefore a decarbonisation lever as much as a commercial one.

Common mistakes with freight accounting

• Using volumetric (dimensional) weight instead of actual weight. Courier invoices often bill by whichever is larger — the actual kilos or a size-based volumetric figure — but tonne-km emissions track real mass. Pulling the billed weight straight off a courier invoice can overstate a bulky, lightweight shipment's footprint by a wide margin.

• Measuring straight-line distance instead of the routed distance. A map's straight line between two ports understates real shipping lanes, which follow coastlines and shipping corridors rather than great-circle routes — the gap is usually a modest understatement, but it compounds across many shipments if applied as a habit rather than corrected.

• Mixing owned-fleet legs into the tonne-km method. If part of a journey — say, the final delivery leg — uses a van your organization owns and fuels, that leg's litres belong in the fleet fuel calculator as Scope 1, not as additional tonne-km here. Running the whole multi-leg journey through the distance-based method double-counts or mis-scopes the owned portion.

• Letting one urgent air shipment hide in an annual total. Because air freight's factor is roughly fifty times sea's, a single expedited shipment can dominate a period's freight number without anyone noticing, since it is easy to log tonnage without separating routine sea freight from occasional air exceptions. Tracking tonne-km by mode, not just as one combined figure, is what surfaces this.

What this calculator doesn't cover

Honesty about limitations is part of the method:

• These are average factors, not your carrier's. Real emissions depend on the specific vessel, aircraft or vehicle, how full it ran, and the fuel it burned. If your carrier provides shipment-level emissions from its own reporting, that figure is more specific than these defaults — use it, and keep the evidence trail.
• Well-to-tank emissions are excluded. The factors cover the transport activity itself; the upstream emissions of producing and delivering the fuel are published separately by DEFRA and are not added here. Companies reporting Scope 3 at full depth include them.
• Distance is yours to estimate. Sea routes are longer than the straight line on a map. Use port-to-port shipping distances for sea, airport-pair distances for air, and actual road routes for trucking — then state your method and apply it consistently year to year.
• Parcels and couriers are approximated. The tonne-km method still works for small consignments (a 30 kg parcel is 0.03 tonnes), but courier networks involve multiple legs and sorting hubs that mode-level averages only roughly capture.
• Your own vehicles don't belong here. Fuel you buy for trucks you operate is Scope 1 — calculate those litres in the fleet fuel calculator instead of estimating them by distance.

Where this fits in your reporting

Third-party freight sits in Scope 3, category 4 — upstream transportation and distribution — under the GHG Protocol. It's the same number ISSB IFRS S2, GRI 305-3, and CDP freight questions ask for, calculated the same way whether the shipper is a manufacturer, an importer, a nonprofit distributing supplies, or a public agency's logistics arm. For anyone moving physical goods, category 4 is routinely one of the largest Scope 3 lines — and it is the one a Singapore-listed customer's questionnaire will ask about in exactly these terms: upstream transportation and distribution, tonne-km by mode.

Those questionnaires travel down supply chains fast, listing or no listing. The cheapest habit is to log tonnes, kilometres, and mode per shipment as the invoices arrive — every figure you need is already printed on them. And when you would rather not type the numbers in at all, upload the freight invoice itself: the same factors are applied to figures read straight off the document, with a confidence score on every extracted field.

Sources

• UK Government (DEFRA/DESNZ), Greenhouse gas reporting: conversion factors — freighting-goods factors (Open Government Licence v3.0): gov.uk/government/collections/government-conversion-factors-for-company-reporting
• GHG Protocol, Corporate Value Chain (Scope 3) Standard and category 4 technical guidance: ghgprotocol.org/standards/scope-3-standard