Calculation Methodology

1. Standards and frameworks

Paspira CarbonLedger calculates greenhouse gas emissions in accordance with the GHG Protocol Corporate Accounting and Reporting Standard (World Resources Institute and World Business Council for Sustainable Development, 2004, revised 2015). This is the most widely used corporate GHG accounting standard globally and forms the methodological basis for most national reporting requirements including SECR and CSRD.

Emission factors are sourced from the UK Government's annual Greenhouse Gas Reporting Conversion Factors publication, issued by the Department for Energy Security and Net Zero (DESNZ), commonly referred to as DESNZ factors. The current version used by this platform is DESNZ 2026 (published 11 June 2026), verified directly against the official full-set workbook and the official flat-format data export, cell by cell — not from memory or a secondary source.

2. Organisational boundary

The organisational boundary is set using the operational control approach as defined in the GHG Protocol. Under this approach, an organisation accounts for 100% of the GHG emissions from operations over which it has operational control — that is, the authority to introduce and implement its operating policies.

This means the inventory includes emissions from all sites, vehicles and operations the organisation controls, regardless of whether it owns them. It excludes emissions from operations where the organisation holds only a financial interest without operational control, such as minority joint ventures.

Organisations reporting as a group may instead select financial control or equity share as their consolidation method. Whichever method is chosen is applied consistently across every entity in the group, as GHG Protocol requires — the platform does not permit a different method per subsidiary.

Reporting period

The default reporting period is the financial year as configured in account settings. Paspira CarbonLedger supports monthly data entry accumulating to an annual total. A complete inventory requires data for all 12 months across all three scopes.

3. Scope definitions

4. Emission factors

All UK emission factors are sourced from the UK Government DESNZ Greenhouse Gas Reporting Conversion Factors, published annually by the Department for Energy Security and Net Zero. Factors are updated in the platform each year when the new DESNZ publication is released (typically June). Paspira CarbonLedger's activity library contains 255 individually verified factors — 252 from DESNZ 2026, 1 from DESNZ 2025 (a waste factor that DESNZ 2026 does not publish), one from the International Energy Agency (world-average grid electricity) and one from the Association of Issuing Bodies (UK residual mix) — split 56 in Scope 1, 34 in Scope 2, and 165 in Scope 3. The table below shows a representative sample; the full library is available directly within the Inventory and Calculator tools.

Each emission factor represents the kilograms of CO2 equivalent (kgCO2e) released per unit of activity. DESNZ factors include CO2, CH4 and N2O components combined into a single CO2e figure using IPCC AR5 global warming potentials, per DESNZ's published methodology. The two non-DESNZ factors are CO2 only — this is stated explicitly wherever they are used.

Category 3 — fuel and energy-related activities

Thirty of the Scope 3 factors cover GHG Protocol Category 3: the upstream emissions of energy already counted downstream. Four things sit under this heading. Well-to-tank (WTT) factors cover extracting, refining and transporting a fuel before it is burnt. Transmission and distribution factors cover the electricity lost in the network before it reached you. A further WTT factor covers the upstream emissions of that lost electricity. District heat carries the same three components. For most organisations Category 3 adds somewhere in the region of 5 to 10% to a footprint, and it is the category auditors most commonly ask about, because the data plainly exists in the same DESNZ publication.

Biofuels are worth singling out. A biofuel’s combustion factor is near zero because the carbon released is biogenic, but its upstream factor is not: growing, processing and transporting the feedstock consumes real fossil energy. Bioethanol burns at 0.00901 kgCO2e per litre and carries 0.61516 upstream — roughly 68 times larger. Wood pellets are about three times their combustion factor. An organisation that reports biofuel combustion without the matching Category 3 line will show a switch to biofuel as far more beneficial than it actually is.

Four fuels are deliberately omitted from the Category 3 set: naphtha, lubricants, refinery miscellaneous and waste oils. DESNZ publishes a WTT value of 0.0 per litre for each, which indicates no per-litre figure is published rather than that the upstream emissions are nil. Recording them as zero would state something the source does not, so they are left out and noted here instead.

Flight factors include Radiative Forcing Index (RFI) uplift and well-to-tank (WTT) emissions per DESNZ 2026 guidance. Waste disposal factors vary substantially by material and disposal method — organic materials in landfill (food waste, household residual waste) carry a far higher factor than inert materials (glass, aggregates) due to methane generation; the figures shown are representative examples, not universal constants. All DESNZ factors are expressed as kgCO2e incorporating CO2, CH4 and N2O using IPCC AR5 100-year global warming potentials, consistent with DESNZ's published methodology for the 2026 factor set.

5. Net-zero trajectory

The science-based target shown on the dashboard and the SBTi page calculates the annual reduction rate required to reach net zero by 2050, consistent with the SBTi Corporate Net-Zero Standard and GHG Protocol guidance.

Residual emissions assumption

Net zero under the GHG Protocol and SBTi Net-Zero Standard does not mean gross emissions reach literal zero. It means emissions are reduced as far as technically and economically feasible, with a small residual fraction addressed through permanent carbon removal or high-quality offsets. Paspira CarbonLedger assumes a residual emissions level of 10% of the base year total — equivalently, a 90% gross reduction — a common simplification for organisations without a custom science-based target or sector-specific residual calculation.

Dynamic rate with a 1.5°C floor

The required annual reduction is derived from the organisation's own base year rather than being a fixed constant: the 90% total reduction is spread evenly across the years remaining to 2050. Because an earlier base year leaves more time, that dynamic rate alone can fall below what a 1.5°C pathway demands — so SBTi's published minimum rates are applied as a floor. Scope 1 and 2 are floored at 4.2% per year (the 1.5°C absolute contraction minimum) and Scope 3 at 2.5% per year (the well-below-2°C minimum). The stricter of the two — dynamic or floor — always governs.

Example

For a 2025 base year, the dynamic rate is 0.90 ÷ 25 = 3.6% per year. The Scope 3 floor (2.5%) is already exceeded, so Scope 3 uses 3.6%. The Scope 1+2 floor (4.2%) is higher than the dynamic rate, so Scope 1+2 uses 4.2%. An organisation with 180.0 tCO2e of Scope 1+2 and 104.5 tCO2e of Scope 3 in that base year would have a current-year target of 172.44t and 100.74t respectively — 273.18 tCO2e in total, against a 284.5 tCO2e baseline.

This is an illustrative pathway for planning purposes, not a validated SBTi commitment. Organisations seeking formal validation should submit targets to SBTi directly.

6. Scenario forecasting

The scenario forecast on the Year-on-Year page projects emissions from the current year to 2030 under four scenarios. All scenarios use a linear annual reduction applied as a constant percentage of the base year total — consistent with SBTi's expression of required rates.

Scenario values are calculated as: projected(year) = base_year_total + (rate ÷ 100 × base_year_total × years_elapsed), floored at zero. These are illustrative projections only and do not constitute a commitment or guarantee of any specific emission outcome.

7. Data quality

Data quality is assessed on two separate axes, which are deliberately not combined into a single number: how COMPLETE and EVIDENCED your inventory is, and how each individual activity quantity was OBTAINED. The first drives the headline score on the dashboard; the second is the ISO 14064-1 tier shown against each entry.

Headline data quality score

The score shown on the dashboard is the unweighted average of two figures, both measured from your actual data rather than modelled or estimated. Completeness is the number of months entered out of the 12 in the reporting year. Evidence coverage is the share of your activity entries that have at least one supporting file attached — an invoice, meter photo or supplier statement. Both are simple, verifiable counts, which is why the score is presented as a real measure rather than an indicative one.

ISO 14064-1 tiers

Separately from the headline score, each activity entry carries a tier from the five-level framework in ISO 14064-1:2018 Annex B, reflecting how the underlying quantity was obtained. This is shown as a badge against entries in the Inventory. It is a different question from completeness — a fully complete inventory built entirely from spend-based estimates is complete but low-tier, and the two figures are reported separately rather than averaged into one number that would hide the distinction.

Factor match quality

A third, narrower axis applies to the emission factor itself rather than to your data: how well-matched the factor is to the activity it is applied to. An official factor can still be a poor match — for example, a world-average grid figure used for an organisation whose own national grid is materially cleaner or dirtier. Factors derived for a non-UK grid (see section 10) are explicitly marked at a lower match quality for this reason, so the reduced precision is visible rather than hidden behind an official-looking number.

A headline score of 80 or above, combined with entries predominantly at Tier 1 or 2, is a reasonable indication that an inventory is in a position to be put forward for third-party assurance under ISAE 3000 or ISO 14064-3. Neither figure is itself a form of assurance.

8. Carbon credit accounting

Carbon credits are used to address residual emissions that cannot be eliminated through direct reduction. Paspira CarbonLedger records credits as purchased (held but not yet retired) or retired. Only retired credits are deducted from gross emissions to calculate the net carbon position.

Credits are tracked in a double-entry ledger: gross emissions are entered as debits, retired credits as offsetting entries, with a running net position. Credits purchased and held in reserve are tracked separately and shown as a runway figure — how many months of current emissions the held credits would cover at the current burn rate. This is an operational planning metric, not an accounting treatment.

Retiring credits equal to 100% of gross emissions is not equivalent to reaching net zero. Under the SBTi Net-Zero Standard, net zero requires approximately 90% gross emission reduction first, with credits and removals addressing only the small residual. The platform reports the two separately and does not treat offsetting as a substitute for reduction.

Accepted credit standards on the platform include Verified Carbon Standard (VCS/Verra), Gold Standard, UK Emissions Trading Scheme (UK ETS), EU Emissions Trading Scheme (EU ETS), and Woodland/Peatland Carbon Code (UK nature-based). Credits should be from projects that are additional, permanent, verifiable and independently audited.

9. Intensity metrics

Intensity metrics normalise absolute emissions against a business activity denominator. Paspira CarbonLedger calculates two intensity metrics required for Streamlined Energy and Carbon Reporting (SECR) and commonly used in TCFD disclosures.

Employee count and turnover are set in account settings. These metrics are required in the Directors' Report for organisations subject to SECR. They are also used in year-on-year comparisons to separate real emission reductions from changes driven by business growth or contraction.

10. Scope 2 dual reporting

The GHG Protocol Scope 2 Guidance (2015) requires organisations to report Scope 2 emissions using both the location-based and market-based methods where feasible. Paspira CarbonLedger reports both side by side; the location-based figure is the one used for headline totals and science-based target tracking, consistent with SBTi requirements.

The location-based method uses the average grid emission factor for the country of consumption — for UK organisations, this is the DESNZ 2026 UK electricity generation mix factor of 0.13096 kgCO2e/kWh. This figure decreased by 26.0% from the 2025 factor (0.17700 kgCO2e/kWh) following a DESNZ methodology change that reduced the data lag used to calculate the grid mix from two years to one, in addition to continued grid decarbonisation — this is a larger, more structural revision than a typical annual refresh, and worth being aware of if comparing year-on-year Scope 2 totals.

Market-based method and the residual mix

The market-based method reflects the electricity an organisation has contractually chosen. Consumption backed by a Renewable Energy Guarantee of Origin (REGO) certificate is zero-rated, as GHG Protocol provides for a legitimate, retired energy attribute certificate.

The remainder — electricity with no certificate attached — is not valued at the ordinary grid average. That average already includes renewable generation other organisations have claimed through their own certificates, so using it would count the same clean electricity twice. GHG Protocol's Scope 2 Quality Criteria instead place the residual mix rate above a plain grid average in the hierarchy of acceptable data sources. Paspira CarbonLedger applies the published UK residual mix figure of 0.29220 kgCO2e/kWh (Association of Issuing Bodies, European Residual Mix 2024 — the most recent published year; AIB publishes approximately 12 to 18 months after the effective year, which is inherent to how the certificate market reconciles rather than a staleness issue on our part). This figure is CO2 only, not full CO2e.

A practical consequence worth understanding: because the residual mix rate is materially higher than the grid average, an organisation with no renewable coverage will see a market-based figure above its location-based figure. That is the intended behaviour of the standard — the market-based method exists precisely to distinguish organisations that have procured clean electricity from those that have not, and a method where doing nothing produced an identical number would defeat that purpose.

Electric vehicles outside the UK

A DESNZ electric or plug-in hybrid vehicle factor is energy consumption multiplied by grid intensity: kgCO2e per km equals kWh per km multiplied by kgCO2e per kWh. The kWh per km is a property of the vehicle, not the country — a given car uses the same energy per kilometre wherever it is driven. Only the grid intensity changes. So for organisations outside the UK, these factors are rescaled rather than withdrawn: the UK grid intensity is divided out to recover the underlying consumption, and the world-average grid intensity is applied in its place.

The recovered consumption is a good check that this is sound rather than merely arithmetically tidy. Battery-electric cars come back at 17.0 kWh per 100km for a mini rising to 31.9 for a sports car, ranking correctly by size and performance and sitting within the real-world range for each class. A worked example: the average BEV car factor of 0.02686 kgCO2e/km implies 20.5 kWh per 100km, which against the world-average grid gives 0.08922 kgCO2e/km. Derived factors are marked at a lower factor-match quality (see section 7), since a world average is less precise than the organisation's own national grid would be. An organisation that knows its national grid factor should enter it as a custom activity for a better result.

One honest caveat specific to plug-in hybrids: their published figure is blended across electric and petrol kilometres using a UK utility factor — an assumption about how much of a typical journey runs on battery. The energy itself is country-independent; that driving-pattern assumption is not. Battery-electric vehicles carry no equivalent assumption.

What cannot be rescaled

District heat and steam is deliberately not rescaled and remains unavailable outside the UK. A heat network is not electricity: the published figure reflects what that specific network actually burns, and UK networks are largely gas CHP where a Danish one may be waste incineration and a Finnish one biomass. There is no universal energy-per-unit-of-heat to recover and no published world-average heat-network intensity to apply. Organisations outside the UK should obtain their heat supplier's own published kgCO2e/kWh and enter it as a custom activity.

The electric-traction rail factors — national rail, London Underground, light rail and tram — are also not rescaled, for a different reason. They are expressed per passenger-kilometre, so they embed occupancy assumptions specific to the UK network, and UK national rail is only partly electrified, meaning the published figure blends electric and diesel traction. Dividing by a grid factor would incorrectly treat the diesel portion as electricity.

11. Limitations and disclaimers

12. Version history