What is CII in shipping, and what does it stand for?

CII stands for Carbon Intensity Indicator. It is an IMO measure of how much CO2 a ship emits for the transport work it performs, applied under regulation 28 of MARPOL Annex VI to ships of 5,000 gross tonnage and above. It is calculated annually and produces a rating from A to E, where A is the best. It is an operational measure, so it reflects how a ship is run rather than how it was built, which is what distinguishes it from EEXI.

How is a ship's CII rating calculated?

Attained CII is annual CO2 emissions divided by capacity times distance sailed: deadweight for bulk carriers, tankers, gas and LNG carriers, container, general cargo, refrigerated and combination carriers, and gross tonnage for ro-ro and passenger ships. The required CII is the 2019 reference line for that ship type and size from IMO resolution MEPC.353(78), reduced by the year's reduction factor. Comparing the attained value against four boundaries set by the ship type's dd vectors in MEPC.354(78) gives a rating from A to E.

What is the CII reduction factor for 2026 and later years?

The reduction factor relative to the 2019 reference line is 5% in 2023, 7% in 2024, 9% in 2025, 11% in 2026, 13.625% in 2027, 16.25% in 2028, 18.875% in 2029 and 21.5% in 2030, under IMO resolution MEPC.400(83) adopted on 11 April 2025. MEPC.338(76) had left 2027 onward unspecified. No factor is set beyond 2030, and the second phase of the CII review began on 1 January 2026.

What happens if a ship gets a D or E CII rating?

A ship rated D for three consecutive years, or E in a single year, must develop a plan of corrective actions in Part III of its Ship Energy Efficiency Management Plan. The commercial consequence usually arrives sooner than the regulatory one, because charterers increasingly specify a minimum CII rating in fixture terms, so a poorly rated vessel competes for a shorter list of cargoes.

Which ships does CII apply to?

CII applies to cargo, ro-ro and cruise passenger ships of 5,000 gross tonnage and above on international voyages, under regulation 28 of MARPOL Annex VI. Bulk carriers, tankers, gas carriers, LNG carriers, container ships, general cargo ships, refrigerated cargo carriers and combination carriers are rated on the AER metric using deadweight. Ro-ro cargo ships, vehicle carriers, ro-ro passenger ships and cruise passenger ships are rated on the cgDIST metric using gross tonnage.

CII rating calculator

CII stands for Carbon Intensity Indicator. It is the IMO’s annual measure of how much CO₂ a ship emits for the transport work it performs, applied under regulation 28 of MARPOL Annex VI to ships of 5,000 gross tonnage and above. Attained CII is annual CO₂ divided by capacity times distance sailed. Compared against the required value for the year, it produces a rating from A to E.

This CII calculator takes deadweight or gross tonnage, distance sailed and the fuel burned over the year. Every ship type covered by regulation 28, with the required value, all four rating boundaries, and what the same vessel rates each year to 2030.

Ship type

Deadweight (DWT)

Distance sailed (nm/yr)

Reporting year

Fuel consumed over the year (tonnes)

Biofuel blends assume the bio component is certified sustainable and sits at the 65% well-to-wake reduction that qualifies it under MEPC.1/Circ.905/Rev.1, blended into HFO by mass. Your certificate decides the real figure and a better one improves the rating. An uncertified blend takes the fossil factor in full, so pick HFO instead.

Uncorrected CII rating (2026)

C3.80 vs 3.71 required
gCO₂ / dwt·nm

Compliant, and close enough to the boundary that a bad quarter moves it.

On identical operations this vessel drops out of C in 2028, because the required intensity tightens every year while the vessel does not.

This is a first estimate, and a detailed analysis may improve it

An accurate assessment needs a voyage-by-voyage breakdown and consumption split by consumer and purpose, because deductions may apply that work in your favour. A verified CII applies the correction factors and voyage adjustments in MEPC.355(78): ice class and distance sailed in ice, ship-to-ship transfer and shuttle tanker operations, and fuel used for cargo cooling on gas carriers, discharge pumps on tankers, boilers and other auxiliary consumption. This page asks only for annual totals, so treat the letter above as the floor rather than the final answer.

See the full breakdown

All four rating boundaries, the reference line and reduction factor behind them, and what this same vessel rates every year to 2030 on unchanged operations.

How a CII rating is calculated

Every constant behind this tool is read from the IMO resolutions themselves rather than from a summary, so the working can be checked line by line.

Fuel becomes CO₂. Each fuel’s annual tonnage is multiplied by its carbon factor: 3.114 for HFO, 3.151 for LFO, 3.206 for MDO or MGO, 2.750 for LNG. These are the tank-to-wake DCS factors, which are not the well-to-wake figures FuelEU Maritime uses.
CO₂ becomes an intensity. Attained CII is grams of CO₂ per capacity-mile. Capacity means deadweight for bulk carriers, tankers, gas and LNG carriers, container, general cargo, refrigerated and combination carriers, and gross tonnage for ro-ro and passenger ships.
The required value comes from 2019. The reference line for each ship type and size is set in IMO resolution MEPC.353(78), adopted 10 June 2022, and reduced by the year’s reduction factor from MEPC.400(83), adopted 11 April 2025: 11% in 2026, then 13.625%, 16.25%, 18.875% and 21.5% through 2030.
Four boundaries decide the letter. The dd vectors in IMO resolution MEPC.354(78) scale the required value into the A/B, B/C, C/D and D/E boundaries for that ship type.

This implementation reproduces the worked example in MEPC.354(78): a bulk carrier with a required CII of 10 gets boundaries of 8.60, 9.40, 10.60 and 11.80, and an attained value of 9.00 rates B.

How to improve a CII rating

CII measures CO₂ per unit of transport work, so it improves in only two ways: burn less fuel for the same voyage, or carry the same cargo over fewer idle miles. The levers that move it most in practice are hull and propeller condition, voyage and speed optimisation, time spent at anchor or waiting, and switching to a fuel with a lower carbon factor.

Timing matters more than most operators expect. Because CII is an annual figure, a change made in July has roughly half the effect on the rating that the same change would have had in January. A vessel drifting toward D in the first quarter is a decision; the same vessel in November is an outcome.

CII rating calculator

How a CII rating is calculated

How to improve a CII rating

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