How to calculate ferry and maritime emissions

Ferry travel appears in enterprise travel programmes serving European markets, island locations, coastal operations or clients with cross-channel or Irish Sea routing. While it typically represents a small share of total Category 6 emissions, it should be included in any complete inventory — and the distinction between foot passenger and car ferry produces materially different figures. This guide covers how ferry emissions are calculated and what data you need.

Where ferry travel fits in Scope 3 Category 6

Business ferry journeys — whether a foot passenger crossing the English Channel, a car ferry to a client site on an island, or a high-speed catamaran on a coastal route — are included in GHG Protocol Scope 3 Category 6. Ferry is a relatively niche mode in most enterprise programmes, but it can be material for organisations with operations in:

• UK – Ireland routing: Holyhead – Dublin, Pembroke – Rosslare, Liverpool – Dublin, and similar routes are commonly used for business travel between the UK and Ireland.
• Cross-Channel: Dover – Calais and Portsmouth – Le Havre are used for car-dependent travel to France and beyond.
• Island and coastal operations: employees serving island clients (Scottish islands, Channel Islands, Faroe Islands, Greek islands etc.) may make regular ferry crossings as part of their standard business travel pattern.

How ferry emissions are calculated

The calculation follows the same approach as other modes:

Method 1: Spend-based (most likely)

Where only expenditure data is available, a spend-based approach using EEIO factors is possible as a fallback, but is significantly less accurate than distance-based and not recommended for reporting where trip-level booking data can be sourced from a TMC or expense system.

Method 2: Distance-based (recommended default)

Ferry uses the distance-based method, applied at the per-passenger level. The key distinction is whether the traveller is a foot passenger or travelling with a vehicle.

Source: DEFRA 2025. Exact car ferry factor varies by vessel and operator. Factors include WTT.

The car ferry factor is approximately 8× higher per kilometre than the foot passenger factor for the driver, because the vehicle occupies significantly more deck space than a person and its full floor area is allocated to the occupant(s). Where employees can travel as foot passengers and hire a car at destination instead, this typically produces lower emissions and may be lower cost.

For some worked real life examples, read this article.

Ferry versus the alternatives

For cross-channel and short sea routes, ferry competes primarily with short-haul aviation and (where available) rail. Compared on a per-passenger basis:

Ferry routing via Calais is approximately 55 km sea crossing + onward surface travel. Short-haul aviation CO₂e based on DEFRA 2025 with 1.7× RF.

Where Eurostar is available, it is substantially lower-carbon than ferry. For routes where no direct rail alternative exists — particularly UK–Ireland crossings — foot passenger ferry is significantly lower-carbon than flying, making it the preferable choice when travel time allows.

Data requirements and reporting

For ferry travel, the inputs needed are: departure port, arrival port, date of travel, and whether the journey is foot passenger or includes a vehicle. Thrust Carbon applies DEFRA ferry factors by route type and passenger category. Where ferry travel is booked through a TMC or expensed directly, Thrust Carbon can integrate with expense data to extract the relevant data points.

Ferry typically represents a small fraction of overall Category 6 footprint, but including it demonstrates inventory completeness — which matters for third-party assurance under CSRD and ISO 14083 reporting.