The Annual Efficiency Ratio variant of the Carbon Intensity Indicator, used for most cargo ships of ≥ 5,000 GT.
Formula
$$ \text{CII}\text{attained} = \frac{\sum_j F_j \cdot C{f,j} \cdot 10^6}{\text{Capacity} \cdot D} $$
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $\text{CII}_\text{attained}$ | Attained Carbon Intensity Indicator | g CO₂ / (cap·nm) | result |
| $F_j$ | Mass of fuel $j$ burned in the reporting year | t | IMO DCS report |
| $C_{f,j}$ | CO₂ conversion factor for fuel $j$ | t CO₂ / t fuel | MEPC.364(79) Table 1 |
| $Capacity$ | DWT (cargo) or GT (passenger / cruise / ro-pax) | t or - | MEPC.337(76) |
| $D$ | Distance travelled in the reporting year | nm | IMO DCS report |
| $10^6$ | Unit conversion tonnes → grams | - | constant |
Units: grams CO₂ per deadweight-tonne-nautical-mile (g / dwt·nm) for cargo ships; g CO₂ / (GT·nm) for ro-pax, ro-ro vehicle carriers, and cruise ships (the cgDIST variant).
Required CII
$$ \text{CII}_\text{required} = a \cdot \text{Capacity}^{-c} \cdot (1 - Z) $$
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $\text{CII}_\text{required}$ | Required Carbon Intensity Indicator | g CO₂ / (cap·nm) | result |
| $a$ | Ship-type reference-line coefficient | - | MEPC.337(76) Table 1 |
| $c$ | Ship-type reference-line exponent | - | MEPC.337(76) Table 1 |
| Capacity | DWT or GT depending on ship type | t or - | MEPC.337(76) |
| $Z$ | Annual reduction factor - 5 % (2023), 7 % (2024), 9 % (2025), 11 % (2026) | fraction | MEPC.338(76) |
Rating boundaries
Compare the ratio $r = \text{CII}\text{attained} / \text{CII}\text{required}$ against four boundaries $d_1 < d_2 < d_3 < d_4$ from MEPC.339(76), which vary by ship type:
| Range | Rating |
|---|---|
| $r \leq d_1$ | A |
| $d_1 < r \leq d_2$ | B |
| $d_2 < r \leq d_3$ | C |
| $d_3 < r \leq d_4$ | D |
| $r > d_4$ | E |
Assumptions built into our calculator
Cfvalues are the MEPC.364(79) defaults; operators must use certified BDN values for regulatory filings.- Voyage adjustments and exclusions (ice, SAR, safety distance) are handled in the separate CII Voyage Adjustment calculator and not applied here automatically.
- The d-vectors embedded in our tool cover the 13 most common ship types; specialised types defer to the MEPC.339(76) consolidated table.
Sources
- IMO Resolution MEPC.336(76) - 2021 Guidelines on operational CII.
- IMO Resolution MEPC.337(76) - Reference lines.
- IMO Resolution MEPC.338(76) - Reduction factors.
- IMO Resolution MEPC.339(76) - Rating boundaries.
- IMO Resolution MEPC.364(79) - Cf factors.