What is an Inventory Management Plan and Why Does it Matter?

Many companies completing a greenhouse gas (GHG) inventory overlook the importance of an inventory management plan (IMP). In this post, I share what an IMP is and why creating one is so important.

A greenhouse gas (GHG) inventory is an important tool for understanding a company’s emissions, offering insight into where emissions come from and what emissions sources are most significant. However, without clear documentation on the inventory’s methodology, companies will struggle to consistently and accurately calculate emissions year over year. This can limit a company’s ability to measure emission reduction progress, report emissions externally, or get an inventory verified.

An inventory management plan (IMP) can help document parts of the GHG inventory methodology not captured in traditional spreadsheets or software and help ensure companies can efficiently and consistently develop GHG inventories each year. Don’t have one? Keep reading to learn more about IMPs!

What's included in an IMP?

An IMP documents how a company calculates and manages its GHG inventory. The level of detail will vary depending on the size and complexity of the organization, but most plans cover three main areas:

1. Inventory boundaries and scope

An IMP should contain a section that describes what is included in the inventory and why. This includes a description of the organizational and operational boundaries, including which entities, facilities, and emissions sources are included or excluded. It should also identify the reporting period, the base year used to track emissions over time, and any relevant reporting requirements or accounting standards.

2. Emissions calculation methodology

IMPs should also explain how emissions are calculated for each source. This includes documentation around the activity data used and where that data comes from, which emission factors are applied, and how the calculations are performed. Any assumptions, estimates, or source specific methodological decisions are also documented. The goal is to provide enough detail for someone else to understand the methodology and reproduce the calculations using the same data.

Note: A GHG inventory may already include much of this supporting documentation, such as calculation spreadsheets, emission factor references, data collection files, and a summary of the methodology. It’s ok to reference the GHG inventory in an IMP and not duplicate documentation.

However, a GHG inventory may not contain all the details needed to fully reproduce the emissions results. For example, a calculation spreadsheet or software export may show how a company's electricity emissions were calculated using consumption data and an emission factor. An IMP would also document where the consumption data comes from, how gaps in data were handled or estimated, who is responsible for collecting data, which emission factor should be used in future years, and how changes in data sources or methodology should be handled.

3. Inventory governance and data management

An IMP should also explain how the inventory is managed. This includes who is responsible for collecting and reviewing data, where supporting records and calculations are stored, how quality checks are performed, and when the inventory is reviewed and updated.

It is also helpful to document how changes to the inventory methodology are approved and when significant changes to the business or calculation methods will trigger a recalculation of historical emissions (note: having a recalculation policy is actually a requirement when setting science-based targets).

Who needs an IMP? Do I still need one if I use software or a consultant?

Any company that prepares a GHG inventory can benefit from an IMP. Without sufficient documentation, a company may struggle to reproduce its inventory or explain changes in emissions. The plan is particularly useful the more complex an organization is, or when multiple people contribute data or perform calculations, as the potential for errors or inconsistencies is higher.

Using software does not eliminate the need for an IMP. Software can help standardize calculations and manage data, but it does not necessarily document why particular boundaries were selected, how missing data is handled, or who is responsible for reviewing inputs. The IMP should capture these company specific decisions, along with instructions for entering data and managing the inventory. Software documentation can be referenced in the IMP for standard calculations rather than duplicated.

The same principle applies when a consultant prepares the inventory. Organizations should request documentation of the methodology and data management process as part of the engagement. Some consultants provide detailed calculation files and supporting documentation, while others provide only summary results or limited explanations of their methods. An IMP can retain key information about historical GHG inventories if the company switches consultants / software or brings the work in house.

How long does an IMP take to create?

The time required depends on the complexity of the inventory, the quality of existing documentation, and how many emissions sources need to be addressed. Developing an IMP alongside the initial GHG inventory is generally the most efficient approach - the information needed for the plan is already being gathered and decisions about boundaries, data sources, and calculation methods are being made. For a relatively straightforward inventory, documenting these decisions may add approximately one to two weeks to the overall project timeline, although more complex inventories may require additional effort.

Once the initial plan is in place, annual updates should generally require less time. Existing documentation can be reviewed and updated to reflect changes in the business, data sources, calculation methods, or reporting requirements. If the methodology remains largely unchanged, these updates may be relatively minor.

Who uses an IMP?

The sustainability team or whoever manages the GHG inventory is the primary user. The plan serves as a guide for preparing the annual inventory, coordinating data collection, and explaining how emissions are calculated. Other internal teams that provide data, such as finance, procurement, facilities, and operations personnel, may also benefit from documentation that clarifies what information is needed, where it comes from, and how it should be provided.

An IMP is also useful for external auditors and verifiers who need to understand the inventory methodology and assess whether calculations are supported by appropriate evidence. Clear documentation can make the review process more efficient, although an IMP alone does not establish that an inventory is accurate or independently verified.

Finally, IT teams can use the plan when organizations want to automate data collection or integrate emissions calculations into existing systems. Understanding which data fields feed into which calculations helps technical teams design systems that support the inventory process.

Is an IMP worth the effort?

Developing an IMP helps improve the consistency, transparency, and long term management of a GHG inventory. It can preserve institutional knowledge, support assurance readiness, and provide a foundation for improving data collection and calculation processes over time.

I always recommend developing IMPs as part of my GHG accounting projects to help clients establish a repeatable process year over year. The goal is not to create documentation for its own sake, but to make GHG accounting easier to manage and more useful to the business.

Don't have an IMP yet? Reach out to Wild Grove Advisors for a free consultation about what documentation would be most helpful for improving your GHG inventory process!