Converts a ship’s attained CII and required CII into the A–E rating that MARPOL Annex VI uses to flag compliance and trigger corrective-action plans.
Open the live calculator. For the attained-CII computation itself, see the CII Attained formula page.
Formula
$$ r = \frac{\text{CII}\text{attained}}{\text{CII}\text{required}} $$
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $r$ | Ratio of attained over required CII | - | result |
| $\text{CII}_\text{attained}$ | Measured operational CII for the reporting year | g CO₂ / (cap·nm) | CII Attained |
| $\text{CII}_\text{required}$ | Target CII for the ship’s type, size and year | g CO₂ / (cap·nm) | CII Required |
| $d_1, d_2, d_3, d_4$ | A–E rating boundaries for ship type | - | MEPC.339(76) Table 1 |
Compare $r$ against the four boundaries $d_1 < d_2 < d_3 < d_4$ from MEPC.339(76) Table 1, which are specific to each ship type:
| $Range$ | Rating |
|---|---|
| $r \leq d_1$ | A - Major superior performance |
| $d_1 < r \leq d_2$ | B - Minor superior performance |
| $d_2 < r \leq d_3$ | C - Moderate (compliant baseline) |
| $d_3 < r \leq d_4$ | D - Minor inferior |
| $r > d_4$ | E - Inferior |
Rating boundaries by ship type
Values embedded in the calculator (consult MEPC.339(76) for the authoritative table):
| Ship type | d₁ | d₂ | d₃ | d₄ |
|---|---|---|---|---|
| Bulk carrier | 0.86 | 0.94 | 1.06 | 1.18 |
| Oil tanker | 0.82 | 0.93 | 1.08 | 1.28 |
| Container ship | 0.83 | 0.94 | 1.07 | 1.19 |
| Gas carrier (≥ 65,000 DWT) | 0.81 | 0.91 | 1.12 | 1.44 |
| Gas carrier (< 65,000 DWT) | 0.85 | 0.95 | 1.06 | 1.25 |
| LNG carrier | 0.89 | 0.98 | 1.06 | 1.13 |
| General / multipurpose cargo | 0.83 | 0.94 | 1.06 | 1.19 |
| Refrigerated cargo | 0.78 | 0.91 | 1.07 | 1.20 |
| Combination carrier | 0.87 | 0.96 | 1.06 | 1.14 |
| Ro-Ro vehicle carrier (PCTC) | 0.86 | 0.94 | 1.06 | 1.16 |
| Ro-Ro cargo | 0.76 | 0.89 | 1.08 | 1.27 |
| Ro-Pax | 0.72 | 0.90 | 1.12 | 1.41 |
| Cruise ship | 0.87 | 0.95 | 1.06 | 1.16 |
Regulatory consequences
| Rating outcome | Required action |
|---|---|
| A, B, or C in any year | No corrective action. Recognition and some port-fee incentives may apply (check ESI / Green Award). |
| D for three consecutive years | Submit a SEEMP Part III corrective action plan to the flag administration, verified at the next survey. |
| E in any single year | Same - SEEMP Part III corrective action plan required. |
The action plan must set out the measures (speed, routeing, hull cleaning, retrofit, alternative fuel) that will return the ship to at least a C rating, with a timetable.
Assumptions and limits
- Boundaries tabled above cover the 13 most-common ship types. Other classes (drillships, FPSOs, naval auxiliaries, etc.) are outside CII scope under MEPC.336(76).
- The calculator treats the inputs as already-finalised (post voyage-adjustment) values. Exclusions for ice, SAR, safety distance, etc., must be applied beforehand; see the (pending) CII Voyage Adjustment & Exclusion calculator.
- Reduction factor Z and reference-line coefficients follow the state of the regulations as of early 2026. If IMO amends post-2026 Z values, update
shared/cii.ts(single source of truth).
Sources
- IMO Resolution MEPC.336(76) - 2021 Guidelines on operational CII.
- IMO Resolution MEPC.337(76) - reference lines.
- IMO Resolution MEPC.338(76) - annual reduction factors Z.
- IMO Resolution MEPC.339(76) - rating boundaries d₁..d₄.
- DNV - CII - Carbon Intensity Indicator.
- ShipCalculators.com guide: What is CII?.