Enter one year of operation: ship type, size, distance sailed and fuel burned. You get the attained and required CII, the rating, how it moves as the reduction factors tighten to 2030, and how much fuel you would need to cut to stay at C.
Fill in the vessel and one year of fuel and distance, then press Calculate. Nothing you enter leaves your browser unless you send it to us with the form below.
| CO₂ emitted | |
| Attained CII | |
| Required CII () | |
| Rating boundaries A | B | C | D | |
| Fuel change to reach C boundary | |
| Approx. speed change for that (same distance) |
Same operation, 2023 → 2030
Estimate only — not an official rating. Correction factors and voyage adjustments allowed under the CII guidelines are not applied. The speed figure assumes fuel per mile varies with the square of speed (cubic power law) — a first approximation, not a vessel-specific result. Reference lines MEPC.353(78), rating vectors MEPC.354(78), reduction factors MEPC.338(76) and MEPC 83, carbon factors per IMO guidelines.
Get a detailed analysis →Beyond the rating
Speed reduction is the blunt answer to a poor CII. Trim optimization, hull and propeller condition, voyage planning and retrofit options are often cheaper per tonne of fuel saved. Our naval architects work from your vessel's own data to show which measures move the rating, and by how much. About our fleet efficiency platform →
FAQ
Attained CII is the CO₂ emitted in a calendar year divided by the ship's capacity and the distance sailed, in grams of CO₂ per capacity-nautical mile. CO₂ is fuel consumed multiplied by the fuel's carbon factor. Capacity is deadweight for most cargo ships and gross tonnage for ro-ro, ro-pax and cruise ships.
The required CII is the IMO reference line for the ship type and size (MEPC.353(78)) reduced by the year's reduction factor. The rating boundaries are the required CII multiplied by the ship-type vectors in MEPC.354(78). A ship rated D for three consecutive years, or E in one year, must submit a corrective action plan.
Relative to the 2019 reference line: 5% in 2023, 7% in 2024, 9% in 2025 and 11% in 2026 (MEPC.338(76)). For 2027 to 2030 the factors agreed at MEPC 83 are 13.625%, 16.25%, 18.875% and 21.5%.
No. The official rating is issued by your flag or recognised organisation from verified IMO DCS data. This calculator gives an estimate and does not apply the correction factors and voyage adjustments allowed under the CII guidelines.
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