> ## Documentation Index
> Fetch the complete documentation index at: https://docs.appliedaifoundation.org/llms.txt
> Use this file to discover all available pages before exploring further.

# 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)](https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MEPCDocuments/MEPC.353\(78\).pdf) — Reference lines (a, c coefficients)
* [IMO MEPC.354(78)](https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MEPCDocuments/MEPC.354\(78\).pdf) — Rating boundaries (d-vector values)
* [IMO MEPC.339(76)](https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MEPCDocuments/MEPC.339\(76\).pdf) — AER/CII calculation guidelines and reduction factors
* [Reefer correction](/methodology/reefer-correction) — MEPC.355(78)
* [Open-IMO-CII-Calculator](https://github.com/Open-IMO/Open-IMO-CII-Calculator) — open-source reference implementation