How to Calculate Green Steel Carbon Intensity

Define the production boundary

Start by choosing the production stage represented in the metric. Crude steel at the caster exit is a common boundary because it captures furnace and ladle metallurgy emissions without double-counting downstream finishing. If you report hot rolled coil or finished products, document the additional processes and adjust emissions accordingly. Clearly distinguish between on-site operations and outsourced steps such as pelletising or galvanizing.

Determine the temporal scope as well. Annual reporting matches most assurance cycles, but quarterly or monthly intensities support dynamic customer contracts. Use the same cadence for production data, electricity metering, and upstream emission factors to maintain internal consistency.

Variables and notation

Track the following symbols with SI-consistent units:

• E_dir – Annual direct (Scope 1) emissions in tonnes CO₂e from furnaces, reformers, and process gases.
• E_elec – Annual electricity-related (Scope 2) emissions in tonnes CO₂e using the selected market-based or location-based factors.
• E_feed – Optional upstream embodied emissions in tonnes CO₂e from purchased pellets, DRI, or alloys allocated to the period.
• C_scrap – Scrap credit in kilograms CO₂e per tonne of steel, representing avoided virgin production.
• Q_steel – Annual steel output in tonnes that matches the reporting boundary.

Ensure emission factors correspond to the production location and timeframe. For example, match renewable power purchase agreements to delivery months before reducing E_elec. When estimating scrap credits, use lifecycle studies relevant to the scrap grade and ensure the same assumption is shared with customers to avoid double counting.

Carbon intensity formula

The intensity calculation aggregates direct, indirect, and optional feedstock emissions, subtracts the scrap credit, and divides by total steel output:

The resulting I_steel is expressed in kilograms CO₂e per tonne. Multiplying by 1000 keeps alignment with customer disclosures and carbon border templates. If the scrap credit exceeds total emissions, the plant effectively delivers a negative intensity; flag such cases for additional review because they typically signal inconsistent boundaries or outdated credit factors.

Step-by-step methodology

1. Collect direct emissions data

Pull E_dir from continuous emissions monitoring systems, stack tests, or natural gas purchase records. Separate combustion of process gases, such as coke oven gas, from auxiliary boilers to maintain transparency. Ensure conversion to tonnes CO₂e includes methane and nitrous oxide if material.

2. Quantify electricity emissions

Combine plant electricity consumption with grid emission factors. When renewable power purchase agreements or time-matched certificates are used, apply the market-based methodology referenced above. Reconcile electricity totals with facility energy management systems to catch metering gaps.

3. Attribute feedstock emissions

If reporting cradle-to-caster intensity, allocate upstream emissions from pellets, DRI, or ferroalloys. Use supplier-specific lifecycle data when available. When suppliers lack primary data, rely on harmonised datasets while documenting the substitution. Align allocations with the tonnage consumed during the reporting period, not purchase dates.

4. Determine scrap credit

Establish C_scrap by referencing lifecycle studies comparing primary and secondary steel. Adjust the credit if scrap requires extra processing, such as stainless segregation or high residual removal. Communicate the chosen credit to customers so their product footprints remain consistent.

5. Validate production output

Confirm Q_steel using caster production records, quality adjustments, and inventory reconciliations. Exclude defective tonnage that is re-melted within the period to prevent double counting. Align the output with the same time window used for emissions.

6. Calculate intensity and segment contributions

After computing I_steel, report the share contributed by Scope 1 versus Scope 2 emissions. This segmentation highlights the impact of furnace fuel switching, hydrogen adoption, or renewable electricity procurement, providing a roadmap for further decarbonization.

Validation checks

Benchmark the resulting intensity against peer facilities or published pathways such as the Mission Possible Partnership. Significant deviations should be explained through furnace technology, charge mix, or grid carbon intensity. Confirm that the scrap credit does not exceed the sum of direct and electricity emissions unless the plant is already net-negative.

Reconcile total emissions with corporate inventories to ensure the steel plant contribution matches enterprise reporting. If the facility exports hot briquetted iron or other intermediates, allocate emissions carefully to avoid double counting when those products are consumed internally.

Limits and interpretation

The method assumes linear relationships between scrap credit and production. In practice, residual elements or scrap availability may limit substitution. Document these operational constraints alongside the intensity result so stakeholders understand improvement ceilings.

Additionally, product-specific certifications such as ResponsibleSteel may require allocating emissions to coil grades or customer orders. Extend the same formula by applying mass-based splits once the plant-level intensity is validated. Pair the greenhouse gas metric with air pollutant monitoring, water usage, or sustainable aviation fuel comparisons from the SAF blend guide when engaging with sustainability-conscious buyers.

Embed: Green steel carbon intensity calculator

Input direct, electricity, and feedstock emissions plus an optional scrap credit to obtain kg CO₂e per tonne and shares by scope.