Free tool · MARPOL Annex VI
Free CII calculator: work out an A to E rating from fuel and distance
Enter the ship type, its size, the distance sailed and the fuel burnt, and see the attained and required CII and the rating band. It needs no account, and the sum runs on your own phone or computer.
Updated · Written by SeaReady in our own words. Not affiliated with OCIMF, RightShip, CDI, any MoU or any administration — always check the current official documents.
Your ship and year
Example figures are filled in. Type your own. Nothing is saved or sent.
Use the total distance travelled in the year, both under way and not under way (MEPC.412(84)).
Fuel burnt in the year (tonnes, as reported for IMO DCS)
Minor inferior
Figures are grams of CO₂ per DWT and nautical mile. This is a working figure, not the official rating.
How the rating is worked out
| Step | Sum | Named source |
|---|---|---|
| CO₂ emitted | Tonnes of each fuel × its CF factor | MEPC.364(79), CF table, used through MEPC.352(78) |
| Attained CII | CO₂ ÷ (capacity × distance) | MEPC.352(78), as amended by MEPC.412(84) |
| 2019 reference line | a × capacity to the power of −c | MEPC.353(78) |
| Required CII | Reference × (1 − Z ÷ 100) | MEPC.338(76) for 2023 to 2026; MEPC.400(83) for 2027 to 2030 |
| Rating A to E | Attained against four boundaries, each d × required | MEPC.354(78), Table 1 |
The reduction factor Z is 5% for 2023, 7% for 2024, 9% for 2025 and 11% for 2026, then 13.625%, 16.25%, 18.875% and 21.5% for 2027 to 2030.
With the example figures, 5,200 t of heavy fuel oil and 400 t of marine gas oil make 17,475.2 t of CO₂. Over 63,500 DWT and 55,000 nautical miles that is an attained CII of 5.00, against 4.35 required for 2026, which rates D. The full explanation is in our CII rating and SEEMP guide.
What it does not do
- It does not apply the correction factors and voyage adjustments of MEPC.355(78), so the official figure may differ.
- It does not check your fuel or distance figures. The official data are the verified IMO DCS figures.
- It does not decide whether CII applies to your ship. The rule covers the listed ship types of 5,000 GT and above (MARPOL Annex VI regulation 28).
- It offers only the years with an adopted reduction factor.
A ship rated D for three years in a row, or E once, needs a corrective action plan in its SEEMP (MARPOL Annex VI regulation 28). Speak to your company about any D or E.
Sources and date
IMO resolutions, opened and read on the IMO site. Checked 9 November 2026.
- MEPC.328(76), June 2021: MARPOL Annex VI regulation 28, which ships are rated and what follows a D or E.
- MEPC.352(78), June 2022: how CII is calculated, with MEPC.412(84), 2026: distance under way and not under way.
- MEPC.353(78), June 2022: reference lines.
- MEPC.354(78), June 2022: rating boundaries.
- MEPC.338(76), June 2021, and MEPC.400(83), April 2025: reduction factors.
- MEPC.364(79), December 2022: fuel CF factors.
- MEPC.355(78), June 2022: correction factors and voyage adjustments, not applied here.
Questions seafarers ask
Is this the official CII rating for my ship?
No. It is a working figure. The official rating is issued by the flag State or its recognised organisation from the verified IMO DCS data, and correction factors may apply.
Which ships does CII apply to?
Ships of 5,000 GT and above of the types in the list, under MARPOL Annex VI regulation 28.
Why are only the years 2023 to 2030 offered?
Those are the years with a reduction factor adopted by IMO. There is no adopted figure yet for later years.
Is my data sent anywhere?
No. The sum runs in your browser and nothing you type is saved or sent.
Use the CII calculator in SeaReady
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Related guides
- CII calculator & rating guideAttained vs required CII, the A–E boundaries, Z factors 2023–2030 and a worked example.
- IMO DCS reporting guideReg. 27 deadlines, MEPC.385(81) data fields, BDN reconciliation and IMO DCS vs EU MRV, ETS and FuelEU.
- Ship bunkering & ECA fuel changeoverPre/during/post bunkering checks, MEPC.182(59) samples, BDNs and 0.10% ECA changeover.