How to Calculate Emissions from a Ferry Journey

Written by Ellen West on 4 Feb 2021

Ferry journeys often accompany road trips or crossings. Calculating the emissions of one is surprisingly simple thanks to the conversion factors provided by the UK Government.

First, you need to find the route distance in question. Ferries do not always travel in a straight line, so it is important to source as accurate a distance as possible. Google Maps will often show you a route distance. There are also other sea distance calculators, such as which may offer more accurate numbers. You can also request this information from your travel provider.

Some sea distance calculators will give you the distance in nautical miles. To convert to kilometres, multiply the number of nautical miles by 1.852.

Once you have the distance, you simply need to multiply the distance in kilometres (km) by the number in the table below.


CO2e per pkm

CO2 per pkm

CH4 per pkm

N2O per pkm

Foot passenger





Car passenger





Average (all passenger)





Note: Units are in per passenger-kilometre (pkm). For example, 2 people travelling 100km would be 200 passenger-kilometres.

Worked example: 2 people travel 50 nautical miles by ferry, on foot. 50 nautical miles is 92.6 kilometres. Since we measure in passenger-kilometres, we need to multiply the kilometres by the number of passengers, to get 185.2 passenger-kilometres. Finally, we multiply this by the number in the table (0.01874) to get 3.47 kg of CO2e.

As you can see, the factors differ depending on how you travel. They are also dependant on the type of greenhouse gas. Best-practice is to calculate CO2e, as it best represents total emissions. CO2e translates to mean ‘carbon equivalent’. As different gases have different warming potentials, CO2e is used to measure all greenhouse gasses to equal effect.

For more examples, here are some carbon emissions calculations on some UK ferry routes:

  • The carbon emissions of Holyhead to Dublin with your car is 13.9 kg of CO2e (107.4 km travelled per passenger).
  • The carbon emissions of Port of Dover to Port of Calais on average is 5.64 kg of CO2e (50 km travelled per passenger).
  • The carbon emissions of Aberdeen to Lerwick (Shetland) on foot is 6.60 kg of CO2e (357.3 km travelled per passenger). This increases to 46.3 kg CO2e if you take the car!

To power this article and our calculation, we have relied upon expert research by the UK Government's Department for Business, Energy & Industrial Strategy, and the Department for Environment, Food & Rural Affairs. The approximate distances have been sourced using Google Maps and


You can find more conversion factors here. For detailed explanations, stay tuned for more data-driven insights from the Thrust Carbon team. Let’s make travel effortlessly green together.