ISO 14064-1:2018 is the second-edition international standard for quantifying and reporting greenhouse-gas emissions at the organizational level. The first edition (2006) used Scope 1, 2, 3 terminology aligned with the GHG Protocol Corporate Standard. The 2018 revision replaced that with six numbered categories: direct emissions (1), indirect from imported energy (2), indirect from transport (3), indirect from products used (4), indirect from products sold (5), and other indirect (6). The categories map roughly onto Scopes 1, 2, and the subdivisions of Scope 3, but the renaming matters for verification language. A GHG report can be ISO 14064-1 compliant and GHG Protocol compliant simultaneously, and most are.
Every inventory starts with a boundary decision. ISO 14064-1 lets you choose either the operational-control approach (you account for emissions from sources you operate) or the equity-share approach (you account for the share of emissions matching your ownership percentage). Most companies pick operational control because it is simpler to audit. The choice is not academic: a holding company with minority stakes in joint ventures can report very different totals depending on which boundary it uses, and the chosen boundary must be disclosed in the inventory report.
For each emission source, ISO 14064-1 expects activity data multiplied by an emission factor. The standard does not prescribe specific factors, but it requires that you document the vintage and source. Common free factor sources include DEFRA (UK Open Government Licence), the IEA emission-factor database, IPCC Assessment Report defaults, EPA eGRID for US electricity, and IDAE for the Spanish grid. Commercial databases like Ecoinvent provide more precise life-cycle factors but are not required, and they cannot be redistributed in public reports without permission.
For refrigerants and fluorinated gases, ISO 14064-1 expects you to use IPCC AR6 GWP100 values rather than older AR4 or AR5 values, although many corporate inventories still use AR5 because their software has not been updated. Reviewers usually accept either, provided the vintage is stated.
An ISO 14064-1 inventory is not just a spreadsheet of numbers. The standard requires an inventory report that documents the organizational and operational boundaries, the methodology choices, the activity data sources, the emission factors and their vintages, an uncertainty assessment, and a year-over-year reconciliation if the inventory has changed methodology. This report is what an auditor reads under ISO 14064-3, and it is also what the Spanish MITECO carbon-footprint registry requests for the "Calculo" seal.
If you need third-party verification, the auditor follows ISO 14064-3. There are two levels of assurance: limited (the auditor states no inconsistencies were found) and reasonable (the auditor states the inventory is materially accurate). Reasonable assurance is more expensive and more common in regulated contexts. The verifier must be accredited under ISO 14065. In Spain, ENAC publishes the list of accredited verifiers. In the UK, UKAS does the same. CDP and SBTi recognize both limited and reasonable assurance, but reasonable is preferred for the highest disclosure scores.
Spain's "Registro de Huella de Carbono" registry hosts inventories aligned with ISO 14064-1 (or the GHG Protocol Corporate Standard plus Scope 2 guidance). For the basic "Calculo" seal, third-party verification is not mandatory, but the methodology and factor sources must be documented and submitted. For the upper-tier seals ("Reduzco" and "Compenso"), verification is increasingly expected. Royal Decree 214/2025 (published in the BOE on 12 April 2025) made carbon-footprint calculation and publication mandatory for large companies - over 250 employees, plus consolidated turnover above 40 million euros or balance-sheet total above 20 million euros, in two consecutive years. Entry in the MITECO registry itself remains voluntary for private entities; the decree mandates the calculation and a reduction plan, not the registration. SMEs are outside the obligation.
The most common failure mode in first-time ISO 14064-1 verification is poor activity-data documentation. The numbers are usually right; the audit trail to invoices and meter readings is not. Other frequent issues are using older AR4 GWPs for fluorinated gases, applying the residual mix instead of the location-based grid factor for purchased electricity, and forgetting to include refrigerant top-ups (which look like maintenance to accounting but are emissions to the auditor). The fixes are not technical, they are procedural: build a documentation routine before the next reporting cycle, not during the audit.