CII Rating Calculator: A to E Carbon Intensity Grade
Enter a ship's attained CII and particulars and get the A to E rating: the required CII for the year, the attained-to-required ratio, where it falls against the MEPC.339(76) band boundaries, and whether a corrective action plan is triggered.
Formula, assumptions, and limits
The rating is the attained CII expressed as a ratio of the required CII, read against the ship-type band boundaries. To find it, divide attained by required and locate the ratio on the d-vector scale:
CII_attained - the year’s operational carbon intensity, gCO₂ per capacity-mile, from the annual fuel and distance. CII_required - the reference line a·Capacity^(−c) reduced by the year’s MEPC.338(76) factor Z. d1..d4 - the rating boundaries for the ship type, from MEPC.339(76).
The d-vectors are the rating’s substance and the reason a single ratio maps to different letters across the fleet (the ro-ro values were revised by MEPC.354(78) in 2022). A bulk carrier crosses from C to D at a ratio of 1.06; a tanker at 1.08; a ro-ro passenger ship not until 1.14. The boundaries encode how much operational variance the IMO treats as normal for each trade, and a charter-party CII clause that quotes a ratio without naming the ship type is ambiguous by construction.
What the rating does not capture: the rating is a year’s verdict, not a trajectory. A ship can be a comfortable C in 2025 and a D in 2026 with identical operation, because the required line moved, and the three-consecutive-years D trigger counts those moving-line years against the ship. The rating also says nothing about why: a poor letter can come from slow trades, long ballast legs, heavy weather, or genuine inefficiency, and the SEEMP Part III plan, not the letter, is where the cause is diagnosed. The calculator computes the letter and the distances to the adjacent bands; the operational story is the user’s.
How to use this calculator
- Select the ship type for its reference coefficients and d-vector.
- Enter the capacity on the correct basis (DWT or GT).
- Select the reporting year for the reduction factor.
- Enter the attained CII.
- Read the rating, the ratio, and the band scale; the highlighted box is the current grade, and the distances to the adjacent boundaries show how much margin the ship holds.
Reading the rating bands
| Rating | Meaning | Action |
|---|---|---|
| A | Major superior performance | None |
| B | Minor superior performance | None |
| C | Moderate performance, compliant | None |
| D | Minor inferior | Corrective plan after three consecutive D years |
| E | Inferior | SEEMP Part III corrective plan immediately |
The asymmetry at the bottom is deliberate: a single E triggers the corrective plan at once, while D is tolerated for two years before the third consecutive D pulls the trigger. The plan is not a penalty in the EU-ETS sense, there is no euro figure attached, but it is an enforceable administrative obligation verified by the flag state, and a ship that ignores it risks the Statement of Compliance the DCS regime hangs on. Charterers increasingly write the rating into the fixture: a clause requiring the ship to maintain at least C, with the owner warranting the operational profile that delivers it, is now standard drafting on period charters.
Common errors
- Comparing ratios across ship types. A ratio of 1.05 is a C on a bulk carrier and on a tanker, but a ratio of 1.07 is a C on the tanker and a D on the bulker; the d-vector, not the ratio alone, sets the letter.
- Reading the letter as durable. The required line tightens every year, so a C with thin margin is next year’s D; the rating is a single year’s verdict, not a standing grade.
- Confusing CII with EEXI. EEXI is the one-time design index; the CII rating is the annual operational grade, and a ship can pass one and fail the other.
- Treating D as a penalty year. A single D carries no immediate obligation; it is three consecutive D years, or one E, that triggers the SEEMP Part III plan.
CII against the EU’s two carbon regimes
A deep-sea ship trading to Europe now answers to three carbon rules at once, and they measure different things. The IMO CII rating grades operational carbon intensity, gCO₂ per capacity-mile, against a tightening line, with an administrative corrective plan as the consequence and no direct price. The EU ETS prices the quantity of CO₂ emitted on EEA-scope voyages in allowances, a euro bill that scales with tonnes. FuelEU Maritime grades the well-to-wake intensity of the energy per megajoule, with a euro penalty for missing a target. A ship can be a clean CII C and still carry a heavy ETS bill simply by trading a lot, or hold a strong CII rating while failing FuelEU on a dirty fuel chain the CII’s tank-to-wake CO₂ factor never sees. The rating on this page is the operational-efficiency letter; the EU ETS calculator and the FuelEU intensity calculator carry the other two, and a fleet plan that optimizes one in isolation usually worsens another.
Why this page returns the IMO’s own grade
The CII rating is the letter that follows a ship through a year of trading, and a charter desk, an operator, and a financier will each recompute it for the same vessel before they act on it. This page returns the IMO’s own grade so those three runs agree: the required CII for the year, the attained-to-required ratio, the band, and the corrective-action threshold, all from the resolution chain rather than a house interpretation of it.
The arithmetic is the MEPC.337/338/339 chain in the shared CII module, so this page, the CII required calculator, and the attained-versus-required calculator cannot disagree on a boundary. The band scale renders the d-vector visually with the current grade highlighted, and the adjacent-band distances turn the letter into an operational target: how much CII to shed to climb, how much margin before a slip.
Where the attained figure itself comes from fuel and distance, the CII attained calculator builds it; where the question is how the grade erodes across the reporting years, the attained-versus-required calculator holds the attained steady and tightens the line.
Further reading
- What is CII?
- CII corrective action plan
- SEEMP I, II and III
- CII required calculator
- CII attained vs required calculator
Frequently asked questions
- How is the CII rating calculated?
- The attained CII is divided by the required CII to give a ratio, and the ratio is placed against the ship-type rating boundaries d1 to d4 from MEPC.339(76). At or below d1 is A, up to d2 is B, up to d3 is C, up to d4 is D, and above d4 is E. The boundaries differ by ship type, so the same ratio can be a C on one ship and a D on another.
- What CII rating do I need to be compliant?
- C or better. A and B are superior performance, C is the moderate-performance compliance line, and D and E are inferior. A ship rated D for three consecutive years, or E for a single year, must develop a SEEMP Part III corrective action plan setting out how it will return to at least C.
- Why does my rating get worse each year without changing anything?
- The required CII tightens annually through the MEPC.338(76) reduction factor, from 5 percent below the reference line in 2023 to 11 percent in 2026, and on to 21.5 percent by 2030 under the MEPC.400(83) factors adopted in 2025. A ship holding its attained CII steady slides toward worse bands as the line moves under it, which is the regulation's design: the operational bar rises every year.
- Is the CII rating the same as the EEXI?
- No. EEXI is a one-time technical index on the ship's design efficiency, certified once. The CII rating is an annual operational measure of how the ship was actually run, recomputed every year from the year's fuel and distance; a technically efficient ship can still earn a poor CII rating by trading inefficiently.
In short
Enter a ship's attained CII and get the A to E rating: required CII, the attained-to-required ratio, the MEPC.339(76) band boundaries, and the corrective trigger.