How is the CII calculated?

The attained operational Carbon Intensity Indicator is total CO2 emitted in the year divided by the ship's deadweight capacity multiplied by the distance sailed, expressed in grams of CO2 per tonne-mile. CO2 is derived from fuel consumed using each fuel's carbon factor. The required CII is the 2019 reference line for the ship type and size, reduced by the annual IMO reduction factor.

What do the A to E ratings mean?

The attained CII is compared with the required CII and placed in one of five bands. A and B are superior, C is the minimum acceptable band, and D and E are inferior. A ship rated D for three consecutive years, or E for a single year, must submit a corrective action plan in its SEEMP before its Statement of Compliance is issued.

Is this calculator accurate enough for reporting?

It is an estimate for planning and screening, not a verified submission. It uses the published IMO reference lines, reduction factors and rating boundaries, but it does not apply ship-specific correction factors, voyage adjustments or exclusions, and verified DCS data will differ. Use it to see where a vessel sits and what would move it; use your verifier for the statutory figure.

How is the EU ETS cost estimated?

Shipping entered the EU Emissions Trading System in 2024 with a phase-in of 40% of verified emissions for 2024, 70% for 2025 and 100% from 2026. Voyages within the EEA count in full and voyages into or out of the EEA count at 50%. The estimate here multiplies your CO2 by the share you enter, by the phase-in percentage, by the allowance price you enter.

How can a ship improve its CII rating?

The largest levers are usually operational rather than technical: speed reduction, better voyage and weather routeing, hull and propeller cleaning, trim optimisation and reduced time at anchor with machinery running. Because CII is a distance-based intensity, improving cargo utilisation and reducing ballast legs also help. Full Ahead Maritime tracks consumption and maintenance against each vessel so the effect of each measure is visible.

Free tool — no sign-up

Free CII calculator — attained CII, A–E rating and ETS cost

Fill in the fields below — attained CII, required CII, the A–E band and the EU ETS allowance cost update as you type.

Georgios Zografos

Chief Engineer · Technical Superintendent · Cyprus

Vessel & voyage data

Ship type

Deadweight (DWT)

Distance sailed (nautical miles / year)

Reporting year

Annual fuel consumed (tonnes)

HFO

VLSFO / LFO

MGO / MDO

LNG

Methanol

EU ETS exposure

Share of CO₂ in EU ETS scope (%)

100% of intra-EEA voyages and port calls, 50% of voyages into or out of the EEA.

Allowance price (€ per tonne CO₂)

Result

Band A for 2026

70% of the required CII

Attained CII: 3.205 g CO₂ / t·nm
Required CII: 4.600 g CO₂ / t·nm
Total CO₂ emitted: 11,526 t
CO₂ to reach band C: Already within band C
CO₂ in EU ETS scope: 4,034 t (100% phase-in)

Estimated EU ETS allowance cost

€282,385

Per year, at €70/tCO₂. Allowance prices move daily.

Estimate only. Uses published IMO reference lines, reduction factors and rating boundaries without ship-specific corrections, voyage adjustments or exclusions. Verified DCS and MRV data will differ — use your verifier for statutory figures.

Track this across your fleet

What the calculator does with your numbers

Fuel tonnes are converted to CO₂ with the MEPC.364(79) carbon factors, then divided by deadweight times distance sailed to give the attained CII in grams of CO₂ per tonne-mile. The required CII comes from the MEPC.353(78) reference line for your ship type and size, reduced by the MEPC.354(78) factor for the reporting year. The ratio between the two is placed in the A–E bands for that ship type. Nothing is sent anywhere — the maths runs in your browser.

The one figure worth acting on is CO₂ to reach band C: the tonnes you would have to stop burning over the year to leave band D. In practice that is speed, routeing, hull and propeller condition, trim and time at anchor with machinery running — which is why the CII number belongs next to the maintenance plan, not in a separate spreadsheet at year end.

Free to reuse · CC BY 4.0

Put this calculator on your own site

The calculator is embeddable and the reference dataset behind it — MEPC.353(78) reference lines, MEPC.354(78) reduction factors, MEPC.364(79) carbon factors and the EU ETS phase-in — is published as open JSON. Use either in a class handout, a company resource page or your own tooling. The only condition is the attribution link.

<iframe src="https://fullaheadmaritime.com/embed/cii-calculator"
  width="100%" height="620" style="border:0" loading="lazy"
  title="CII rating and EU ETS cost calculator"></iframe>

Preview the widget Open JSON dataset

Cite as: Full Ahead Maritime, CII reference dataset, CC BY 4.0, fullaheadmaritime.com/cii-calculator

Carbon intensity is only half the 2026 bill. Our EU ETS methane cost study shows 359 LNG-signature ships — 2.1% of the EEA-trading fleet — carrying 78% of the new methane liability, from verified MRV filings.

CII and EU ETS questions.

Keep your results

Have this sent to you, with what usually comes next.

A copy of your attained CII, required CII and A–E rating, plus the reduction factors for 2026 and 2027 so you can see where the rating goes if nothing changes.

Now: your rating summary and the 2026/2027 reduction factors.
Day 3: the four operational levers that move a D-rated ship back to C, with the assumptions behind each.
Day 8: how CII, EU ETS and FuelEU interact on the same voyage — one worked example.

Rate the whole fleet, not one vessel at a time.

Full Ahead Maritime keeps continuous CII and EU ETS accrual against every vessel alongside planned maintenance and statutory compliance. Start with a 30-day parallel review alongside your current system.

Start a 30-day parallel review See pricing

Proof, not a bullet point

Everything on this page keeps working with the link down.

Cut your connection and try it

Open the CII calculator, turn off Wi-Fi, keep typing. The arithmetic runs in your browser — no request leaves the device. That is the same engine the vessel app uses at sea.

Installable on the vessel PC

Full Ahead Maritime installs as an app and caches your fleet, jobs, certificates and evidence locally, so a superintendent can work a full day with no link at all.

A sync outbox, not lost work

Work done offline is queued and lands ashore in order when the link returns — over VSAT, Starlink or a two-minute port window.

Try the offline calculators How the offline layer is built

Next step · one real vessel

You just ran the numbers. Want to keep the work with the vessel record?

The calculator works on figures you typed. A 30-day parallel review lets your team examine its attained and required CII, the band it lands in, and the EU ETS bill that follows alongside the maintenance and compliance record it already keeps.

Start a parallel review See founding-fleet terms

Ran the CII calculator? Mention it in the note and I will start from those figures.