Scope 1 Iron & Steel Process Calculator (BOF / EAF / DRI / Sinter / Coke — IPCC Vol 3 Ch 4)

What the iron & steel process calculator does

This calculator computes the Tier 1 Scope 1 process emissions of iron and steelmaking: the CO₂ released by reducing iron ore and refining crude steel, plus the minor methane from sintering and coke-making. You enter the tonnage produced at each step — sinter, pellet, coke, pig iron, DRI, crude steel — and the engine multiplies each by its IPCC 2006 default factor and sums the lines into one process total, with a firewall that stops the same iron being counted twice.

Process CO₂, not combustion CO₂

The defining boundary of this tool is process versus energy. Process emissions come from the chemistry — carbon in coke and other reductants combining with oxygen stripped from iron ore, and carbon removed from the melt during refining. They occur whether or not any fuel is separately metered. The emissions from burning fuel to heat the furnaces are energy emissions, and they belong in a stationary-combustion inventory, not here. IPCC 2006 Volume 3, Chapter 4 governs the process side; the combustion side sits under Volume 2 (Energy). Keeping them apart is what prevents the most common steel double-count.

Tier 1 — production times a default factor

The arithmetic is deliberately simple: tonnes produced at a step, multiplied by the default emission factor for that step, in tonnes of CO₂ per tonne of product. That is the IPCC Tier 1 method. It does not model your specific coke rate, ore grade, or reductant mix — those are Tier 2 and Tier 3 refinements that require site data the default method does not carry. What Tier 1 gives is a defensible, standardised first figure, computed identically for every mill, which is exactly what a screening estimate or a cross-check against a more detailed inventory needs.

The double-counting firewall — one steel line, not the whole chain

The instinct on first use is to add a line for every step in the works: sinter, coke, pig iron, then crude steel. For an integrated mill that is wrong, and it is the single error this calculator is built to catch. The crude-steel factors for the basic-oxygen and open-hearth routes already include blast-furnace ironmaking. Adding a separate pig-iron line on top counts the same iron twice.

The pig-iron rule — why BOF is one line

The basic-oxygen factor of 1.46 t CO₂ per tonne of crude steel is a route factor: it spans the blast furnace and the converter together. The standalone pig-iron factor of 1.35 exists for mills that produce and sell merchant pig iron, not for adding underneath a BOF line. So an integrated blast-furnace-to-BOF mill enters only the BOF line for its steelmaking. If you add pig iron as well, the engine treats it as a conflict, excludes the pig-iron line from the total, strikes it through in the breakdown, and shows a banner explaining why. An override exists for the genuine merchant-iron case — iron sold or used separately, not converted into your own steel — which demotes the block to an advisory and includes the line.

Aggregate versus disaggregated — the global-average conflict

A second block guards the global-average factor. The 1.06 t CO₂ per tonne global-average-steel value is a blended figure — roughly 65% BOF, 30% EAF, 5% OHF on a 2003 vintage — meant as a standalone screening number when you do not know your route split. It cannot sit alongside a route-specific line, because that mixes an aggregate with its own disaggregated parts. If both are present the engine excludes the aggregate line and keeps the route-specific detail.

The combinations that are valid

Not every multi-line ledger is a conflict. A mill running more than one route enters each route on its own tonnage — BOF, EAF, and OHF lines can coexist because each covers a distinct slice of production. A direct-reduced-iron route into an electric arc furnace is valid as a DRI line plus an EAF line: the DRI line is the iron source, and the EAF factor excludes blast-furnace iron, so the two do not overlap. Upstream sinter, pellet, and coke lines can sit alongside any steel line. The firewall blocks only the genuine overlaps, not legitimate multi-step ledgers.

The boundary error that costs the most is not a wrong factor — it is the right factor applied twice. An integrated mill’s iron is already inside its steel. Count the route, not the chain, and the firewall keeps the total honest.

BOF vs EAF vs DRI–EAF — the route decides the footprint

Before any tonnage is entered, the route sets the order of magnitude. The basic-oxygen route reduces iron ore with coke in a blast furnace — carbon-intensive chemistry, and the bulk of a steelmaker’s process CO₂. The electric-arc route melts scrap with electricity, skipping ore reduction almost entirely, so its process emissions are small and its real footprint moves to Scope 2. Direct reduction sits between them, using natural gas to reduce ore into a solid feed for an arc furnace.

Why an EAF total looks low — and why that is correct

An electric-arc mill that reports 0.08 t CO₂ per tonne of process emissions has not understated anything. Its emissions are overwhelmingly indirect: the carbon intensity of the grid powering the furnace. That belongs in Scope 2, computed from electricity consumption and a grid factor, and it is reported there, not here. The split is the point — this calculator isolates the process side so that the route comparison is clean. An honest EAF process figure is a small one; the lever for an arc mill is decarbonising its power, which a process calculator cannot show.

The process steps and their emission factors

Every factor below is an IPCC 2006 default from Volume 3, Chapter 4, read live from MasterBrain at calculation time. They divide into upstream preparation (sinter, pellet, coke), ironmaking (pig iron, DRI), and steelmaking (BOF, EAF, OHF), plus a small set of methane factors and one blended aggregate.

The methane lines — and two units that trip people up

Sintering and coke-making release small amounts of methane alongside the CO₂. The calculator carries three CH₄ factors, and two of them have units that are easy to mis-state. Coke-oven methane is 0.1 grams per tonne of coke — grams, not kilograms — so it is genuinely tiny. DRI methane is published per terajoule of reductant energy (1.0 kg CH₄ per TJ NCV), not per tonne of DRI, which means it cannot be derived from DRI tonnage alone and the calculator does not present a per-tonne DRI methane figure. Sinter methane is the one straightforward per-tonne value, at 0.07 kg per tonne of sinter.

Methane converts to CO₂e through its global-warming potential: 28 on the AR5 100-year basis the calculator defaults to, or 29.8 on AR6. The CO₂ lines carry a GWP of 1 and are never reweighted. Because the methane contribution is so small for iron and steel — well under a percent of the total for a typical mill — the AR5-versus-AR6 choice barely moves the headline figure, but it is recorded for consistency with the rest of an inventory.

How the calculation works

Each line follows the same short path: pick the process step, enter the tonnage produced, and the engine reads the default factor live, multiplies, and adds the line to the total — after the firewall has checked the selected set for conflicts. A route preset can seed a conflict-free set of lines for you; from there you adjust tonnages and add any upstream steps.

What you enter, what the engine derives

You enter production tonnages — tonnes of crude steel by route, tonnes of sinter, pellet, coke, pig iron, or DRI. The engine derives everything else: the per-line CO₂ as tonnage times factor, the methane lines converted to CO₂e at the selected GWP basis, the firewall exclusions, and the summed process total. Nothing about the chemistry is yours to supply at Tier 1 — the default factors carry it.

The one operation — tonnage times factor

For a CO₂ line the calculation is tonnes produced times the factor in tonnes of CO₂ per tonne of product. For a methane line it is tonnes produced times the factor (converted to a consistent mass), times the methane GWP, divided to tonnes of CO₂e. The firewall sits between the lines and the total: it does not change any individual line’s arithmetic, it decides which lines are allowed to contribute. That separation — correct per-line maths, boundary-checked summation — is what makes the headline figure both accurate and non-overlapping.

Worked example — an integrated BF-BOF mill

A worked inventory shows the method and the firewall together. The mill below is an integrated blast-furnace-to-BOF works producing five million tonnes of crude steel a year, with its own sinter plant. The factor values are live MasterBrain figures; the production tonnages are illustrative inputs. The basis is AR5 for the methane conversion.

The process ledger

^† If a pig-iron line is added to this integrated mill, the firewall excludes it and strikes it through — the 1.46 BOF factor already includes blast-furnace ironmaking, so a separate 1.35 pig-iron line would double-count it. This is the firewall doing its job, not an error. Coke is left out here because the site reports it in its combustion inventory (Energy-1A); include it only if it is not already counted there. Factor values via MasterBrain v2026.262, IPCC 2006 Vol 3 Ch 4.

Every figure reconciles as tonnage × factor; only the production tonnages are illustrative. The methane line is ≈0.1% of the total — immaterial but reported for completeness. The 1.62 intensity exceeds the bare 1.46 BOF factor because the sinter plant’s emissions are spread over the same crude-steel output. The CH₄ conversion uses AR5 (28); on AR6 (29.8) the sinter CH₄ line rises to ≈8,344 t CO₂e, moving the total by ≈500 t — negligible at this scale.

The EAF contrast

Run the same calculator for a one-million-tonne electric-arc mini-mill melting scrap, and the process total is 1,000,000 × 0.08 = 80,000 t CO₂e — eighty kilotonnes against the integrated mill’s eight megatonnes. The arithmetic is not the story; the boundary is. The mini-mill’s dominant emissions are the electricity driving its furnace, which sit in Scope 2 and never appear in this calculator. A clean process comparison between the two routes is only meaningful with that exclusion stated plainly.

Reading the result — where the process carbon sits

For an integrated mill, the steelmaking route dominates and everything upstream is a thin band on top. The chart below shows the contribution split for the worked example — the BOF line against the sinter CO₂ and the immaterial sinter methane. The shape is typical of blast-furnace steel: the route factor carries almost the entire process footprint.

Process contribution split of the worked integrated mill (8,107,840 t CO₂e). Bar widths are proportional to each line’s share. This is one mill’s inventory, not a sector benchmark — an EAF or DRI–EAF mill would show a completely different shape, and the route mix dominates everything. Figures are engine output, reconciled vs MasterBrain v2026.262.

Tier 1 versus Tier 2/3 — accuracy and when each applies

The IPCC framework offers three tiers of increasing accuracy and data demand. This calculator is Tier 1 throughout, and saying so plainly is part of using it correctly. A Tier 1 number is a standardised default; a Tier 2 or Tier 3 number is your plant’s actual chemistry. They answer different questions.

The honest framing is that a Tier 1 figure and a Tier 2/3 figure for the same plant will differ — sometimes materially, because coke rates, ore grades, and reductant mixes vary widely from the IPCC default. The calculator carries a standing note to that effect and does not present its output as a measurement. Use it where a default is appropriate: a screening estimate, a sanity check on a more detailed inventory, or a first pass before a site builds its carbon balance.

Process versus energy emissions — the boundary that trips audits

This calculator covers only the Scope 1 process CO₂ from ironmaking and steelmaking. For the full cradle-to-gate embodied carbon of steel and aluminium — which adds the energy, raw-material and EN 15804 module emissions a purchaser reports as Scope 3 — see the embodied-carbon methodology.

The second firewall is conceptual rather than coded: the line between process emissions and energy emissions. Iron and steel inventories fail review when the two are mixed — either by leaving process CO₂ out because the fuel was already counted, or by counting the coke twice, once as a process input and once as a combustion fuel.

What belongs here, and what belongs in the combustion calculator

Process emissions — the CO₂ from reducing ore and refining steel — belong in this calculator. The combustion of fuels to heat furnaces, generate steam, or run mobile plant belongs in a stationary or mobile combustion inventory under IPCC Volume 2. The awkward case is coke. Coke is both a reductant (process) and, where its carbon ends up as energy, an energy carrier. The calculator carries the coke line as an opt-in Energy-1A item precisely because many sites already capture coke in their combustion inventory; including it here as well would double-count. Only add the coke line if your coke-making CO₂ is not already in your energy figures.

The audit failures to pre-empt

Reporting context — EU ETS, CBAM, IPCC inventories, SBTi steel

Iron and steel process emissions feed several reporting and regulatory regimes, and the tier and boundary that satisfy each one differ. A Tier 1 screening figure is a starting point for all of them and a sufficient figure for none of the regulated ones — the table sets out which is which.

For the corporate roll-up that consolidates this process figure with energy and indirect emissions into one organisational total, the process line carries into the GHG inventory aggregator as a Scope 1 entry. For the regulated reporting that sits downstream, the EU ETS allowance calculator and the EU CBAM calculator work from their own monitored or regulatory-default figures rather than this Tier 1 default.

Data sources, model, and factor basis

The complete underlying reference — every factor in this section, versioned with full source provenance and downloadable as CSV with a citable Zenodo DOI — is published as the IPCC industrial-process (IPPU) emission factors dataset.

The model — source and structure

The calculator reads its factors from the metals.iron_steel.* keyspace in MasterBrain, sourced from IPCC 2006 Guidelines Volume 3, Chapter 4 (Metal Industry Emissions), Tables 4.1 and 4.2. Every row is a Scope 1 process factor — the emissions occur at the producing facility. There is no separate factor table inside this tool; the factors resolve live by key at calculation time, so a figure computed today and the same figure recomputed after a data-layer release are distinguishable by the MasterBrain version stamped on the output.

No fallback floor — em-dash on miss

Unlike fuel and grid factors, the industrial-process factors carry no hardcoded fallback value. This is deliberate. If a factor cannot be read from MasterBrain, the calculator renders an em-dash rather than a stale or invented number — the house rule across GreenCalculus value lookups. The only hardcoded constant in the engine is the methane global-warming potential (28 on AR5, 29.8 on AR6), which mirrors the GWP table. So the canonical values are exactly those in the factor table above, rendered live; there is no second set of floor values to reconcile against.

GWP basis and completeness

The CO₂ lines that make up almost the entire footprint carry a GWP of 1 and are never reweighted. The methane lines convert at 28 (AR5) or 29.8 (AR6) per the methane GWP, selectable to match the rest of your inventory; the choice barely moves the total because methane is well under a percent of iron and steel process emissions. There is no nitrous oxide factor for this category in IPCC Vol 3 Ch 4 — a genuine completeness fact, recorded so a reviewer knows N₂O was considered and is not applicable, rather than overlooked. For the underlying warming-potential values, see the IPCC AR6 GWP values reference; coke and other carbon reductants are discussed in the coal glossary entry.

A dedicated iron & steel process methodology page sets out the IPCC tier structure, the reductant carbon-balance approach, and the route boundaries in full; it is a roadmap page and will be linked here when it publishes.

Related process calculators

This calculator is the first of the industrial-process tools and the iron & steel entry point. The process figure it produces is a Scope 1 line that consolidates into a full corporate inventory, and it sits alongside the regulated-reporting tools that work from monitored or border-adjustment figures.

For the organisational roll-up that brings this process total together with energy and value-chain emissions, the GHG inventory aggregator consolidates Scope 1, 2, and 3 into one boundary total. For the regulated reporting that steel installations face, the EU ETS allowance calculator works from verified installation emissions, the EU CBAM calculator handles import declarations on the EU border-adjustment factors, and UK operators report combined energy and process figures through the UK SECR calculator. The other industrial-process calculators cover the rest of the IPPU fleet: the aluminium smelting PFC calculator, the cement & lime process calculator, the chemicals process calculator, the glass & ceramics process calculator, and the semiconductor etch-gases calculator. For other Scope 1 fugitive and fluorinated sources, the coal mine methane calculator covers mine ventilation and degasification CH₄, and the F-gas inventory aggregator rolls up HFC, PFC, SF₆, and NF₃ emissions.

Frequently asked questions

Methodology notes and limitations

Scope and purpose. This calculator computes the Tier 1 Scope 1 process emissions of iron and steelmaking — CO₂ from ore reduction and steel refining, plus minor sintering and coke-making methane — under IPCC 2006 Guidelines Volume 3, Chapter 4. It is a process-emissions tool: it does not compute the energy emissions from fuel combustion, which belong in a separate stationary or mobile combustion inventory under IPCC Volume 2.

Method — production times default factor. Each line is production tonnage multiplied by an IPCC default factor in tonnes of CO₂ per tonne of product. Methane lines convert to CO₂e at the methane GWP (28 on AR5, the default; 29.8 on AR6). CO₂ lines carry a GWP of 1 and are not reweighted. This is the Tier 1 method throughout.

The double-counting firewall. A boundary guard runs over the selected line set. It blocks a blast-furnace pig-iron line beneath a BOF or OHF line (the route factors already embed ironmaking), with an override for genuine merchant iron; it blocks the global-average-steel aggregate alongside any route-specific line; and it advises on cases needing care. Valid multi-line combinations — multi-route mills, DRI plus EAF, upstream steps alongside any route — are allowed. The firewall decides which lines contribute to the total; it does not alter any line’s arithmetic.

Tier boundary. The calculator is Tier 1 only. Carbon-balance and reducing-agent mass-balance methods (Tier 2 and Tier 3) are out of scope and flagged in-tool. A Tier 1 default will differ — sometimes materially — from a plant’s site-specific figure; the output is a screening estimate and a cross-check, not a measured inventory.

Methane units and completeness. Coke-oven methane is published in grams per tonne of coke (0.1 g), not kilograms. DRI methane is per terajoule of reductant energy, not per tonne of DRI, and is not derived from DRI tonnage. There is no nitrous oxide factor for this category in IPCC Vol 3 Ch 4 — a completeness fact, recorded as considered and not applicable.

Factor basis and live reads. Factors resolve live from the metals.iron_steel.* MasterBrain keyspace (source IPCC 2006 Vol 3 Ch 4, Tables 4.1/4.2) at calculation time, and the MasterBrain version is stamped on the output for restatement work. The industrial-process factors carry no hardcoded fallback floor: a failed read renders an em-dash, never a fabricated value. The only hardcoded constant is the methane GWP.

Coke as Energy-1A. The coke line is opt-in because coke carbon is most often captured in a site’s energy inventory. Include it here only if your coke-making CO₂ is not already counted in your combustion figures; including it in both double-counts.

No regulatory substitution. Results are Tier 1 estimates and do not constitute a verified inventory or an assurance opinion. For EU ETS installations a Tier 3 carbon balance is generally required; for CBAM declarations the EU Annex I default factors apply, not these IPCC factors. Review by a qualified practitioner is required before use in any regulated filing.