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Open IMO Carbon Intensity Indicator (CII) Calculator 🚢

What is this?

An unofficial open source implementation of the International Maritime Organisation (IMO)'s Carbon Intensity Indicator (CII).

The CII indicator aims to make the carbon intensity of any given ship easy to understand, transparent, and standardised. It does so by ranking all ships globally on an A to E rating (A being the best, E being the worst). Ship emission intensity calculations consider a mixture of weight, distance travelled in the calendar year, and the fuel used in their main engines (for a comprehensive explanation, see the methodology section).

Each grade from A to E, coloured gradually from green to red

Grades are re-calculated annually. The boundaries of what is considered "good" is a moving target, described in table 4. This moving target is intended to encourage shipping firms to constantly improve the carbon intensity of their ships to 2030. The graph below demonstrates the gradual tightening of the IMO's Carbon Intensity requirements over time. The nearer to 2030, the lower a ship's Attained CII must be to achieve an A grade.

A graph showing the gradual

The specification for this software can be found in IMO's resolution MEPC.354(78), adopted in June 2022. Additional references, summaries, & resolutions can be found in the References & datasets section.

Note

The repository code & software is provided as-is. While best-efforts are made to ensure its results are acurate inline with the IMO's CII specifications, the results it produces are estimates and guidance. Results should not be considered proof of regulatory compliance.

Table of Contents

Software

Software Roadmap

The following features are on the roadmap for the application:

  • Support for Dependency Injection (DI). Currently the application does not
  • Support for IMO Resolution MEPC.355(78). Currently the application considers fuel consumption only. Support for MEPC355(78) will bring additional CII properties, for example the lighting in crew quarters.

Getting Started

The library can be installed via Nuget. There is a C# dotnet console app at EtiveMor.OpenImoCiiCalculator.DemoConsoleApp, which demonstrates how to create a new instance of the calculator, submit data, and receive results in the format EtiveMor.OpenImoCiiCalculator.Core.ModelsCalculationResult.

When submitting data to the CalculateAttainedCiiRating method, the following parameters are required:

ShipType shipType,          
double grossTonnage,       
double deadweightTonnage, 
double distanceTravelled,   
TypeOfFuel fuelType,       
double fuelConsumption,  
int targetYear
  • The ship's type must be one of EtiveMor.OpenImoCiiCalculator.Core.Models.Enums.ShipType.
  • Gross Tonnage is measured in long-tons (1.016047 metric tonnes, or 1,016.047 kilograms)
  • Deadweight Tonnage is measured in long-tons (1.016047 metric tonnes, or 1,016.047 kilograms)
  • Distance travelled is measured in nautical miles (1,852 metres)
  • Fuel type must be one of EtiveMor.OpenImoCiiCalculator.Core.Models.Enums.TypeOfFuel
  • Fuel consumption is measured in grams, and accepts scientific notation like 1.9e+10
  • Year must refer to the measured year. For example, if a ship's fuel consumption is known in 2022, all other results will be based from that point

Multiple Fuel Type calculations

There are two CalculateAttainedCiiRating methods. One for a ship which consumes a single fuel type, and another which consumes multiple fuel types. Both methods are available at CalculateAttainedCiiRating.

Calculator Result Format

{
    "results": [
        {
            "isMeasuredYear": true,                        
            "isEstimatedYear": false,                     
            "year": 2019,                                 
            "rating": 2,                                   
            "requiredCii": 19.184190519387734,    
            "attainedCii": 16.243733333333335,
            "attainedRequiredRatio": 0.8467249799733408,
            "calculatedCo2eEmissions": 60914000000.0,
            "calculatedShipCapacity": 25000.0,
            "calculatedTransportWork": 3750000000.0,
            "vectorBoundariesForYear": {
                "year": 2019,
                "shipType": 110,
                "weightClassification": {
                    "upperLimit": 0,
                    "lowerLimit": 2147483647
                },
                "capacityUnit": 3,
                "boundaryDdVectors": {
                    "Superior": 14.579984794734678,
                    "Lower": 17.649455277836715,
                    "Upper": 21.869977192102013,
                    "Inferior": 24.939447675204054
                }
            }
        },
        ...
    ]
}
Property Description
isMeasuredYear describes if the result array was generated based on this year
isEstimatedYear describes if the result array was NOT generated based on this year (is always equal to !isMeasuredYear)
year describes the year in question
rating describes the rating for the ship in the given year. A=1, B=2, C=3, D=4, E=5. 0 indicates an error. See EtiveMor.OpenImoCiiCalculator.Core.Models.Enums.ImoCiiRating
requiredCii The actual intensity required for the ship to be considered in-range of the IMO's regulations (note that from 2027 onwards, this is a projection)
attainedCii The estimated or actual intensity attained for the ship in the given year
attainedRequiredRatio The ratio between requiredCii and attainedCii
calculatedCo2eEmissions The calculated CO2e emissions this result was based on
calculatedShipCapacity The calculated ship capacity this result was based on
calculatedTransportWork The calculated transport work this result was based on
vectorBoundariesForYear.year the year in question (repeats .year)
vectorBoundariesForYear.shipType the type of ship EtiveMor.OpenImoCiiCalculator.Core.Models.Enums.ShipType
vectorBoundariesForYear.weightClassification the weight classification the ship has been considered for (see MEPC.354(78))
vectorBoundariesForYear.capacityUnit describes if this ship was measured against its Deadweight or Gross Tonnage EtiveMor.OpenImoCiiCalculator.Core.Models.Enums.CapacityUnit
vectorBoundariesForYear.boundaryDdVectors.Superior Describes the highest value a ship't attainedCii can acheive, while still being considered Superior
vectorBoundariesForYear.boundaryDdVectors.Lower Describes the highest value a ship't attainedCii can acheive, while still being considered Lower
vectorBoundariesForYear.boundaryDdVectors.Upper Describes the highest value a ship't attainedCii can acheive, while still being considered Upper
vectorBoundariesForYear.boundaryDdVectors.Inferior Describes the highest value a ship't attainedCii can acheive, while still being considered Inferior

Methodology

A ship's Carbon Intensity Indicator (CII) is measured by calculating its transport workload in a given calendar year, then calculating the mass of $CO_2$ produced by the ship in that year. The ship's Attained CII is the product of its $transportWork$ and the $massOfCO_2Emissions$ in one calendar year.

$AttainedCII = massOfCo2Emissions \times transportWork$

Ships are split into 12 categories, for example "Bulk Carrier", "Tanker", "Cruise Passenger Ship" among others (see Table 1 for a comprehensive list). A ship is compared internally among its category peers but never across categories, for example, a Bulk Carrier is not directly comparable to a LNG Carrier in this system.

Inputs

  • The type of ship
  • The type of fuel used by the ship's main engine
  • The capacity of the ship, measured in either Deadweight Tonnage (DWT) or Gross Tonnage (GT)
  • The distance travelled by the ship in one calendar year, measured in nautical miles

The ship's Attained CII is then compared to its Required CII to produce an easy to understand grade for the ship. The grading scheme is in the range A to E, where A is the most efficient bracket, C represents a ship at-or-near its CII, and E is the least efficient.

Grade Description
A CII below the Superior Boundary
B CII above the Superior Boundary and below the Lower Boundary
C CII between the Lower Boundary and the Upper Boundary
D CII above the Upper Boundary and below the Inferior Boundary
E CII above the Inferior Boundary

Graphical representation of IMO's ship boundaries, indicating the CII requirements to attain an A, B, C, D, E grade

Fig1. IMO Boundaries, after IMO MEPC.354(78)

Ship Grade Ratio Methodology

A ship's grade is calculated by comparing its Attained CII to its Required CII to give its performance $A/R$ ratio. If the ship's $A/R$ ratio falls below the boundary for its class of Ship Type, it attains a higher (better) grade. Boundaries are calculated as:

$shipTypeRequiredCII \times exp(d_i)$.

Ship Grade Worked example

The worked example below considers a Bulk Carrier, with a Deadweight Tonnage below 279,000. Assuming the Bulk Carrier's $required CII$ is:

$10g CO_2 / DWT.NM$

Important

For some ship types, $GT \times NM$ should be used instead of $DWT \times NM$, see Table 1 and transport work done methodology for a comprehensive guide.

Then the boundaries are calculated with:

  • $10 \times exp(d1)$
  • $10 \times exp(d2)$
  • $10 \times exp(d3)$
  • $10 \times exp(d4)$.

The $exp(d_i)$ rating boundaries for each ship type can be found in Table 3. The resultant boundaries for the Bulk Carrier in question are:

Boundary Type Required CII Boundary's Lower Threshold
Superior $= 10 \times exp(d1)$
$= 10 \times 0.86$
$= 8.6$ 		$8.6 gCO_2/transportWork$
Lower $= 10 \times exp(d2)$
$= 10 \times 0.94$
$= 9.4$ 		$9.4 gCO_2/transportWork$
Upper $= 10 \times exp(d3)$
$= 10 \times 1.06$
$= 10.6$ 		$10.6 gCO_2/transportWork$
Inferior $= 10 \times exp(d4)$
$= 10 \times 1.18$
$= 11.8$ 		$11.8 gCO_2/transportWork$

Grades are then derived from these boundaries, by comparing the ship's Attained CII to the thresholds across a given calendar year:

Grade Higher than Lower than Description
A 8.6 Below Superior Boundary
B 8.6 9.4 Above Superior Boundary,
Below Lower Boundary
C 9.4 10.6 Above Lower Boundary,
Below Upper Boundary
D 10.6 11.8 Above Upper Boundary,
Below Inferior Boundary
E 11.8 Above Inferior Boundary

Example Results:

  • If the ship's Attained CII was $9gCO_2/ DWT \times NM$, the ship receives a grade B, as its Attained CII was above the threshold for Superior Boundary, but below the threshold for Lower Boundary.
  • If the ship's Attained CII was $11gCO_2/ DWT \times NM$, the ship receives a grade D, as its Attained CII was above the threshold for Upper Boundary, but below the threshold for Inferior Boundary.

Ship Attained Carbon Intensity Methodology

A ship's Attained carbon intensity is calculated by taking the mass of its aggregate CO2 emissions in a calendar year, and multiplying it by its transport work done in the calendar year.

$massOfCo2Emissions \times transportWork$

Method accepts:

Method Returns:

  • A double representing the ship's Attained Carbon Intensity

Implementation:

Returns the product of a ship's mass of $CO_2$ emissions and its $transportWork$.

Ship transport work methodology

A ship's transport work is calculated by taking its capacity and multiplying it by the distance sailed in nautical miles in the calendar year.

$capacity \times distanceSailed$

Method accepts:

  • capacity the ship's capacity for cargo or passengers
  • distanceSailed the distance sailed in Nautical Miles in the calendar year

Implementation:

Returns the product of a ship's capacity and its distance sailed

Ship CO2 Emissions Methodology

The sum of a ship's $CO_2$ emissions over a given year are calculated by multiplying the mass of consumed fuel by the fuel's emissions factor. If the ship consumes multiple fuel types, the calculation is repeated for each fuel type & consumption mass, then those results are summed together.

Method Accepts:

  • fuelType, an enum derrived from Table 2's Fuel Type column
  • fuelConsumptionMass, a double representing the mass of fuel consumed in grams (g) over the given year

Method Returns:

  • A double representing the $M$ mass of $CO_2$ emitted by the ship across one calendar year

Implementation:

The sum of $CO_2$ emissions $M$ from fuel consumption in a given calendar year is

$M = FC_j \times C_{f_j}$

Where:

  • $j$ is the fuel type
  • $FC_j$ is the mass in grams of the consumed fuel type j in one calendar year
  • $C_{f_j}$ is the fuel oil mass to CO2 mass conversion factor, given in Table 2's $C_F$ column

Ship Capacity Methodology

A ship's capacity is measured by either its Deadweight Tonnage (DWT) or Gross Tonnage (GT). The only exception is Bulk Carriers, which have a capacity capped at 279,000.

To calculate a ship's Capacity in accordance with the IMO's MEPC353(78) guidelines:

Method accepts:

  • shipType, an enum, derrived from Table 1's Ship Type column
  • deadweightTonnage, the deadweight tonnage of the ship, provided in long tons
  • grossTonnage, the gross tonnage of the ship, provided in long tons

Method returns:

  • a double representing the ship's capacity in imperial long tons

Implementation:

$Capacity$ of a given ship is calculated using the following rules:

  • If the ship is a Bulk Carrier, and its DWT is 279,000 or above, its capacity is capped at 279,000
  • If the ship is a Bulk Carrier, and its DWT is below 279,000, its capacity is equal to its DWT
  • If the ship is a Ro-ro cargo ship (vehicle carrier), a Ro-ro passenger ship or a Cruise passenger ship, its capacity is equal to its Gross Tonnage
  • Otherwise, the ships capacity is equal to its DWT

The full implementation detail can be found in Table 1's Ship Type, Ship weight, and Capacity columns.

Exceptions:

  • ArgumentOutOfRangeException is thrown if the DWT is set to 0, when ship type is set to anything other than Ro-ro cargo ship (vehicle carrier), Ro-ro passenger ship or Cruise passenger ship
  • ArgumentOutOfRangeException is thrown if the GT is set to 0, when ship type is set to Ro-ro cargo ship (vehicle carrier), Ro-ro passenger ship or Cruise passenger ship

Reference Tables

Table 1: MEPC.353(78) - Shipping Capacity Tables

The following table describes how to determine a given ship type's Capacity.

Table Source: IMO: MEPC.353(78)

Ship Type Conditional Specification Capacity $a$ $c$
Bulk carrier 279,000 DWT and above 279,000 4,745 0.622
Bulk carrier Less than 279,000 DWT DWT 4,745 0.622
Gas carrier 65,000 and above DWT 14405E7 2.071
Gas carrier Less than 65,000 DWT DWT 8,104 0.639
Tanker DWT 5,247 0.610
Container Ship DWT 1,984 0.489
General cargo ship 20,000 DWT and above DWT 31,948 0.792
General cargo ship Less than 20,000 DWT DWT 588 0.3885
Refrigerated cargo carrier DWT 4,600 0.557
Combination carrier DWT 5,119 0.622
LNG Carrier 100,000 DWT and above DWT 9.827 0.000
LNG Carrier 65,000 and above, less than 100,000 DWT 14479E10 2.673
LNG Carrier less than 65,000 DWT DWT 14779E10 2.673
Ro-ro cargo ship (vehicle carrier) 57,700 and above 57,000 3,627 0.590
Ro-ro cargo ship (vehicle carrier) 30,000 and above, less than 57,700 3627 5,739 0.590
Ro-ro cargo ship (vehicle carrier) less than 30,000 GT 330 0.329
Ro-ro cargo ship GT 1,967 0.485
Ro-ro passenger ship Ro-ro passenger ship GT 2,023 0.460
Ro-ro passenger ship High-speed craft designed to SOLAS chapter X GT 4,196 0.460
Cruise passenger ship GT 930 0.383

Table 2: MEPC.364(79) Mass Conversion between fuel consumption and CO2 emissions

The following table describes how to convert from the fuel used by a ship's main engine $ME_{(i)}$ to the amount of $CO_2$ produced. Fuel consumption is measured in grams (g), as is the output $CO_2$ emission

Table source: IMO: MEPC.364(79)

ID Fuel Type Source/Reference Carbon Content $C_F (\frac{t-CO_2}{t-Fuel})$ Lower calorific value (kJ/kg)
1 Diesel / Gas Oil ISO 8217 Grade DMX to DMB 0.8744 3.206 42,700
2 Light Fuel Oil (LFO) ISO 8217 Grade RMA to RMD 0.8594 3.151 41,200
3 Heavy Fuel Oil (HFO) ISO 8217 Grade RME to RMK 0.8493 3.114 40,200
4a Liquified Petroleum (Propane) Propane 0.8182 3.000 46,300
4b Liquified Petroleum (Butane) Butane 0.8264 3.030 45,700
5 Ethane - 0.7989 2.927 46,400
6 Liquified Natural Gas (LNG) n/a 0.7500 2.750 48,000
7 Methanol n/a 0.3750 1.375 19,900
8 Ethanol n/a 0.5217 1.913 26,800

Table 3: MEPC.339(76) - Ship Grading Boundaries

The following table describes the $dd$ vectors used to determine the rating boundaries for ship types. The columns $dd$ $exp(d_i)$ values represent the boundaries the IMO's rating system in the baseline year (2019).

Table source (2022): IMO: MEPC.354(78) Previous source (2021): IMO: MEPC.339(76)

Id Ship Type Weight Classification Capacity in CII Calculation dd vector exp(d1) dd vector exp(d2) dd vector exp(d3) dd vector exp(d4)
1 Bulk Carrier DWT 0.86 0.94 1.06 1.18
2.a Gas Carrier 65,000 DWT and above DWT 0.81 0.91 1.12 1.44
2.b Gas Carrier Less than 65,000 DWT DWT 0.85 0.95 1.06 1.25
3 Tanker DWT 0.82 0.93 1.08 1.28
4 Container Ship DWT 0.83 0.94 1.07 1.19
5 General Cargo Ship DWT 0.83 0.94 1.06 1.19
6 Refrigerated Cargo Carrier DWT 0.78 0.91 1.07 1.20
7 Combination Carrier DWT 0.87 0.96 1.06 1.14
8.a LNG Carrier 100,000 DWT and above DWT 0.89 0.98 1.06 1.13
8.b LNG Carrier Less than 100,000 DWT DWT 0.78 0.92 1.10 1.37
9 Ro-ro Cargo Ship (Vehicle Carrier) GT 0.86 0.94 1.06 1.16
10 Ro-ro Cargo Ship GT 0.76 0.89 1.08 1.27
11 Ro-ro Passenger Ship GT 0.76 0.92 1.14 1.30
12 Cruise Passenger Ship GT 0.87 0.95 1.06 1.16

Table 4: Annual Carbon Reduction Factors (Z%)

The following table describes the reduction factor to be applied to a ship's $requiredCII$ on an annual basis. IMO have to date released figures up to 2026. In the table, the values from 2027 onwards are unofficial estimates based on the pattern to 2026. IMO aims to release new reduction factors

Table Source: IMO: MEPC.338(76)

Year Reduction factor
Relative to 2019		 Estimated Reduction Factor
2019 0% -- %
2020 1% -- %
2021 2% -- %
2022 3% -- %
2023 5% -- %
2024 7% -- %
2025 9% -- %
2026 11% -- %
2027 -- % 13%
2028 -- % 15%
2029 -- % 17%
2030 -- % 19%

Table 5: Common shipping measurement conversions

Often in shipping, non-metric measurements are used. Conversions are detailed below

Measure Metric Measure Notes
Deadweight Tonne (DWT) $1016.0469088kg$ DWT is a ship's total weight excluding boiler water, measured in Imperial long tons
Gross Tonne (GT) $1016.0469088kg$ GT is a ship's area, measured in Imperial long tons
Nautical Mile (NM) $1.852km$, $1,852m$ NM is equal to 1 minute of latitude at the equator. $1NM = 1.5078 miles = 1.852km$

Shipping Terminology & Glossary

Term Description Notes
Carbon Dioxide Equivalent (CO2eq, CO2, CO2e, $CO_2$) A ship's carbon dioxide emissions Expressed in this implementation in grams (metric)
Carbon Intensity Index (CII) The relative measure of a ship's carbon dioxide emissions, taking distance travelled and fuel type used into account
Deadweight Tonnage (DWT) The measure of a the total contents of a ship, including cargo, fuel, crew, passengers, and water (Excludes water in a ship's boiler) Expressed in long tons (British Imperial)
Final Draft International Standard (FDIS) A draft status for an ISO Standard, indicating the standard is in its final stage of approval
Gross Tonnage (GT) A ship's internal volume Expressed in long tons (British Imperial)
International Maritime Organisation (IMO) A UN Agency responsible for regulating maritime transport rules & regulations
International Organization for Standardization (ISO) Independent, non-governmental, international standard development organization
Liquefied natural gas (LNG) Gas, compressed into liquid form for easier transport
Nautical Miles (NM, nmile) Distance travelled over water, different to land measured miles (statute miles) Expressed in minutes of latitude at the equator
Resolution MEPC.353(78) Internationally standardised reference guide to shipping carbon intensity
Roll-on-roll-off (Ro-ro, Roro, Ro ro) A ship designed to take cargo which can be wheeled (or rolled) in and out of a cargo hold

References & datasets

Further Reading

Useful datasets (mixed public and private)