# How is the score computed?
These grades are completely unofficial and subject to change. Here is the arbitrary non-linear scale I unilaterally:
- A: 0-158 g·CO₂/km/person
- B: 158-268 g·CO₂/km/person
- C: 268-536 g·CO₂/km/person
- D: 536-1071 g·CO₂/km/person
- E: 1071+ g·CO₂/km/person
These bounds have been chosen to match with averages for other transport modes, as computed by the ADEME. We therefore show these scores accompanied by a short explanation text:
- A: better than an average personal car
- B: better than an average plane
- C: 1 to 2 times an average plane's emissions
- D: 2 to 4 times an average plane's emissions
- E: over 4 times an average plane's emissions
You can have a look at this notebook to see the kind of computing I made to choose these bounds so that there are still ships in all bins.
Please reach out if you think we can do better.