How Long a GHG Inventory Takes for an SME — and What You Must Provide (2026)

Quick answer: there is no single "X weeks" that is right for every company. The length of a GHG inventory project for an SME is decided by the number of sites, the quality of your invoices and records, and how far you go into Scope 3 — not by how fast the consultant works. The longest part is almost always on your side: gathering enough activity data (electricity bills, fuel logs, transport records, waste records). This article breaks down the five phases, lists exactly what your company must provide, and points to the step that consumes the most internal effort — so you know what you are signing up for before you sign.

Last updated: 12 Aug 2026.

The short version for busy readers

Six things to remember before starting an inventory:

• Duration is not fixed. It is a function of the data you already have, not a date the consultant promises. Anyone quoting "8 weeks for every company" is guessing.
• The process, however, is standardized. The same five-step framework under the GHG Protocol and ISO 14064-1:2018 applies to every company; what changes is the volume of data.
• Most of the work is yours, not the consultant's. The consultant calculates and reports; you supply the raw data. Slow data means a slow project.
• Collecting activity data is the most time-consuming step. Not the calculation, but chasing invoices and records scattered across departments.
• Scope 3 is the biggest variable. Measuring Scope 1 and 2 is tidy; extending into the value chain (Scope 3) can double the workload.
• Independent verification is a separate step. If a customer or law requires third-party assurance, add time for one cycle under ISO 14064-3:2019.

Key facts — each line is verifiable:

• The most widely used measurement standard is the GHG Protocol Corporate Accounting and Reporting Standard, covering the seven Kyoto Protocol greenhouse gases (CO₂, CH₄, N₂O, HFCs, PFCs, SF₆ and NF₃).
• The organization-level counterpart is ISO 14064-1:2018 — the current edition (confirmed 2024-10-14) — for quantifying and reporting an organization's GHG emissions and removals.
• Purchased electricity, steam, heat and cooling (Scope 2) are handled by the GHG Protocol's 2015 Scope 2 Guidance.
• The value-chain portion is measured per the Corporate Value Chain (Scope 3) Standard, split into 15 upstream and downstream categories.
• Verification and validation of emissions statements follow ISO 14064-3:2019 — a separate step, distinct from writing the report.

Why there is no fixed "X weeks"

The blunt answer: duration is a function of data, not of the consultant's calendar. A single site with complete 12-month electricity bills and no Scope 3 finishes far faster than a company with three plants, missing fuel records, and a duty to declare supply-chain emissions to EU customers. Same consultant, same method — the two projects differ in time mainly because of the quality and readiness of the input data.

This is not a hedge to dodge commitment. It reflects the nature of an inventory: you multiply activity data (litres of oil, kWh of electricity, kilometres of transport) by emission factors. The multiplication is a computer's job and takes hours; hunting down enough activity data is what takes weeks. So instead of asking "how long", the more useful question is "what state is my data in".

International standards deliberately describe an inventory as a repeatable process, not as a deadline. The GHG Protocol Corporate Standard and ISO 14064-1:2018 set out the steps and principles (completeness, consistency, transparency, accuracy) so two different companies still produce comparable results — but neither says how many days it "should" take. Anyone quoting one hard number for all cases is selling false certainty. If you want the detailed Scope 1/2/3 method first, read our guide on GHG inventory Scope 1-2-3 for SMEs; this article focuses on effort on both sides and timeline.

The five phases: what the consultant does, what you do

An inventory project moves through five fixed phases, and at each the split of responsibility is clear: the consultant builds the method and does the maths, the company provides raw data and confirms the boundary. Reading the table below tells you when you are the bottleneck and where to concentrate internal effort.

Table 1 — The five phases of an inventory and who does what

Phase	Consultant does	Company provides / decides	Output
1. Define boundaries	Propose the consolidation approach (financial/operational control); map the organization and operations	List of legal entities, sites, equipment; decide scope (include Scope 3 or not)	Approved boundary map
2. Collect activity data	Issue templates; guide formats; flag gaps	Electricity, fuel, refrigerant, transport, waste records… (see checklist below)	Monthly/annual activity-data table
3. Select emission factors	Choose official factors (national/IPCC); state source and year	Confirm fuel/technology specifics if any	Factor and source list
4. Calculate and allocate by scope	Multiply data × factor; assign to Scope 1/2/3; cross-check	Explain anomalies (usage spikes, missing figures)	Emissions-by-scope table
5. Report and verify	Write the report to standard; support independent assurance if needed	Approve the report; file with authorities if in scope; decide on third-party verification	GHG inventory report (with assurance opinion if any)

The key point: only phases 1, 3, 4 and the reporting part of phase 5 are consultant-driven and reasonably predictable in time. Phase 2 — data collection — sits with the company, and it usually decides the whole schedule. If independent verification is triggered, it follows ISO 14064-3:2019 for verification and validation and is a separate cycle with a third party, not an overlap with writing the report.

What your company must provide — the data checklist

This is the part you prepare, and preparing it early shortens the project the most. Most of the data you already have — in invoices, ledgers, operating logs — but it is scattered across departments and formats. The table groups it by emission source, with the specific records, the matching scope, and the department that usually holds it — use it as a pre-kickoff checklist.

Table 2 — Activity data the company must prepare

Data group	Records to submit	Scope	Usual owner
Purchased electricity	12 months of electricity bills (kWh, not just the amount)	Scope 2	Accounting / admin
On-site fuel combustion	Invoices/logs for diesel, fuel oil, LPG, coal, gas for boilers, furnaces, generators	Scope 1	Engineering / operations
Owned vehicles and machinery	Petrol/diesel logs for company vehicles, forklifts, site machines	Scope 1	Operations / fleet
Refrigerants	Recharge records for air-conditioning and cold storage (refrigerant type, top-up volume)	Scope 1	Engineering / maintenance
Outsourced transport	Logistics records: distance, weight, mode (road/sea/air)	Scope 3 (cat. 4/9)	Procurement / export-import
Operational waste	Waste-collection contracts and records, treatment method (landfill/incineration/recycling)	Scope 3 (cat. 5)	Health, Safety & Environment (HSE)
Purchased materials	Volume and type of main raw materials (if measuring a material Scope 3 category)	Scope 3 (cat. 1)	Procurement
Travel and commuting	Business travel (flights, stays) and employee commuting if in scope	Scope 3 (cat. 6/7)	HR / admin

Two practical notes. First, you need quantities, not just amounts of money: emission factors apply to kWh, litres, kilograms, tonne-kilometres — a bill that only shows money has to be back-converted, which is slow and error-prone. Second, you do not need to measure all 15 Scope 3 categories at once: the Corporate Value Chain (Scope 3) Standard lets you screen and focus on the material categories — usually materials and transport — before expanding. This is also the data EU customers ask for; see our CBAM compliance guide for SME exporters.

Which step consumes the most internal time

The blunt answer: phase 2 — collecting activity data — is almost always the bottleneck. Not because it is technically hard, but because the data is fragmented: accounting holds the electricity bills, engineering holds the boiler logs, procurement holds the transport records, HSE holds the waste files. An inventory forces you, for the first time, to pull it all into one consistent table, in the right units, covering 12 months — and that is internal coordination, not something the consultant can do for you.

Why does this step tend to drag? Three recurring causes in SMEs. One, the data exists but in awkward form — paper invoices, loose files, only monetary amounts. Two, there are gaps — a few months missing, sub-meters not read, rented vehicles that do not separate fuel. Three, no one has been named as the point of contact, so each department answers at its own pace. In our delivery experience, most of a project's elapsed time is spent here, while the calculation and reporting steps are relatively fast and predictable. (An observation from consulting practice, not a published statistic.)

The most effective way to shorten it is not to push the consultant to run faster, but to do three internal things: name a single data owner with authority to request from departments; digitize invoices by quantity (kWh, litres) alongside the money value; and scope Scope 3 realistically from the start instead of expanding midway. These decide the timeline more than any contract clause.

Five variables that decide project length

To estimate whether your own project will be short or long, score it against the five variables below rather than asking for one generic number. The more variables lean to the "lengthens" column, the longer the project — and vice versa.

Table 3 — Five variables that decide inventory duration

Variable	Shortens when	Lengthens when
Number of sites / entities	One location, one entity	Several plants, several subsidiaries, different provinces
Quality of invoices / records	Full 12 months, already digital, recorded by quantity	Missing months, paper only, money-value only
Scope 3 coverage	Scope 1 + 2 only, or 1-2 material categories	Many value-chain categories, dependent on supplier data
Internal owner and coordination	A coordinator in place, departments respond fast	No owner, data arrives in dribs and drabs
Independent verification requirement	Internal report only	Customer/law requires third-party assurance (ISO 14064-3)

For Vietnamese SMEs, there is one more layer of context: if your facility falls under the mandatory scope of Decree 06/2022/ND-CP on mitigation of greenhouse gas emissions, then the inventory is not only about internal pace but tied to statutory filing deadlines — the thresholds and facility list are covered in our Scope 1-2-3 method guide. Planning your data early both shortens the project and avoids a last-minute sprint before the deadline.

Anti-greenwashing: commit only to what you can measure

A good inventory project does not promise a pretty number — it promises a correct one. Time pressure sometimes tempts teams to fill data gaps with estimates and publish them as if measured. That is a legal risk: under Vietnam's Environmental Protection Law 2020, Advertising Law and Consumer Rights Protection Law 2023, disclosures and advertising about environmental attributes must be substantiated and must not mislead.

So the right principle when data is missing is to state the gap and the estimation method, to be transparent about scope (which Scope, which period the figure covers), rather than papering over it with a guess and staying silent. A "carbon neutral" claim that counts only Scope 1 while ignoring Scope 2 and 3 is misleading. An honest inventory report — one that knows what is certain and what is estimated — is worth far more than a polished figure that collapses under assurance. To turn these numbers into a report you can disclose to partners, see ESG reporting with GRI and ISSB.

Through our Green Transition Advisory pillar, GROW works with SMEs from building the data checklist and naming an owner, through inventory under the GHG Protocol/ISO 14064-1, to preparing figures for EU customers and CBAM. Book a free consultation and we will quickly assess your data readiness and estimate a realistic timeline.

Bottom line: the length of a GHG inventory project for an SME is decided by the quality of the company's own activity data and the breadth of its Scope 3 — not by a fixed number of weeks; preparing invoices by quantity and naming one data owner are the two things that shorten the project the most.