Answer
The unit of EEDI is grams of CO₂ per tonne-nautical mile, or g CO₂/tonne-mile. It represents the design carbon efficiency of the ship. The unit of EEOI is also grams of CO₂ per tonne-nautical mile, or g CO₂/tonne-mile, but it represents the actual operational carbon efficiency based on fuel consumed, cargo carried and distance sailed. For passenger ships or special ship types, the denominator may be capacity-mile instead of tonne-mile.
Both indexes share an identical base mathematical structure representing carbon emissions relative to transport work:
EEDI (Design Index) Unit:
EEOI (Operational Indicator) Unit: