CII formulas

Reference-line formula, ship-type constants, rating boundaries, and reduction factors used by the CII engine.

This page documents the exact formulas and constants used in src/lib/utils/ciiCalculator.ts.

Reference CII

CII_ref = a × Capacity^(-c)

Capacity is DWT for cargo and tanker types, GT for cruise ships. Constants are taken from IMO MEPC.354(78).

Ship type	Capacity	a	c
Container	DWT	1,984	0.489
Bulk Carrier	DWT	4,745	0.622
Tanker	DWT	5,247	0.610
Gas Carrier	DWT	14,405	0.807
LNG Carrier	DWT	9,827	0.718
General Cargo	DWT	588	0.388
Ro-Ro	DWT	2,023	0.460
Cruise	GT	930	0.383

Vessel type strings from the database are normalised case-insensitively and matched against synonyms (e.g. “Crude Oil Tanker” → TANKER, “Car Carrier” → RO_RO).

Required CII

Required CII = Reference CII × (1 − reduction_factor)

Reduction factors per MEPC.338(76):

Year	Reduction
2019	0% (baseline)
2020	1%
2021	2%
2022	3%
2023	5%
2024	7%
2025	9%
2026	11%
2027	13%
2028	15%
2029	17%
2030	19%
2031+	19% + 2% per year (extrapolation)

Attained CII

Attained CII = (Total CO₂ in grams) / (Capacity × Distance NM)

CO₂ is supplied in tonnes and converted internally (× 1,000,000).

Rating boundaries

Ratings A–E are determined by multiplying the Required CII by ship-type-specific d-factors (boundary multipliers from MEPC.354(78)):

Ship type	d1 (A)	d2 (B)	d3 (C)	d4 (D)
Container	0.83	0.94	1.07	1.19
Bulk Carrier	0.86	0.94	1.06	1.18
Tanker	0.82	0.93	1.08	1.28
Gas Carrier	0.81	0.91	1.12	1.44
LNG Carrier	0.89	0.98	1.06	1.13
General Cargo	0.83	0.94	1.06	1.19
Ro-Ro	0.66	0.90	1.11	1.37
Cruise	0.87	0.95	1.06	1.16

Rating boundary X = Required CII × d_X

A rating is the highest band that the Attained CII fits within:

• Attained ≤ d1 × Required → A
• Attained ≤ d2 × Required → B
• Attained ≤ d3 × Required → C (this is the compliance threshold)
• Attained ≤ d4 × Required → D
• Otherwise → E

Compliance margin

Compliance margin = Required CII − Attained CII

Positive margin = the ship is below the required line (good). The compliance status is COMPLIANT if Attained ≤ Required, otherwise NON_COMPLIANT.

Implementation

src/lib/utils/ciiCalculator.ts — exports calculateCII, calculateCIISafe, calculateCIIWithReeferCorrection, and calculateCIIWithReeferCorrectionSafe.

Safe variants return null instead of throwing when inputs are missing — used throughout the app where data quality varies by vessel.

Reference

• IMO MEPC.353(78) — Reference lines (a, c coefficients)
• IMO MEPC.354(78) — Rating boundaries (d-vector values)
• IMO MEPC.339(76) — AER/CII calculation guidelines and reduction factors
• Reefer correction — MEPC.355(78)
• Open-IMO-CII-Calculator — open-source reference implementation