GHG inventory checklist: the 10 steps to a defensible first emissions report

A greenhouse gas inventory checklist has ten steps: set your organizational boundary, list the emission sources in each scope, gather the activity data you already hold, choose and document emission factors, calculate Scope 1 from fuel, Scope 2 from electricity, and Scope 3 from spend, then quality-check, document the method, and get it ready for assurance. Done in that order, a first inventory is a data-gathering project, not a research project, because most of the inputs are already in your fuel invoices, utility bills and accounts payable file.

The mistake that turns a three-week job into a three-month one is starting with data collection before you have set the boundary and found the hotspots. Set the frame first, screen with the data you have, then spend effort only where the emissions actually are. Here is the checklist, step by step.

1. Set the organizational boundary

Decide which legal entities and facilities are inside the inventory and write down why. The GHG Protocol gives you two approaches: operational control, where you count every source you operate, and equity share or financial control, where you count by ownership. Most companies use operational control because it is simpler and matches how they run. The choice matters for joint ventures, leased buildings and leased vehicles, so record it once and apply it consistently across every site.

2. List the emission sources by scope

Walk each facility and write down what emits. Scope 1 is anything you burn or leak on site: gas boilers, furnaces, fleet fuel, generators, refrigerant. Scope 2 is the electricity, steam, heating and cooling you buy. Scope 3 is everything up and down the value chain: purchased goods and services, freight, business travel, commuting, waste and, for some firms, use of sold products. You are not measuring yet, just building the map of where numbers will come from. For the full breakdown, our guide to the 15 Scope 3 categories lists them all.

3. Gather the activity data you already have

The inputs for a first inventory are almost all documents you already keep: natural gas and diesel invoices, utility bills showing kilowatt-hours, refrigerant service logs, fuel-card statements, and the accounts payable export that lists every supplier you paid. Pull twelve months of each. Much of this starts life as a PDF, so if your bills and supplier invoices are locked in scanned documents you can convert those PDF statements into a clean spreadsheet before you start classifying, which saves hours of retyping.

4. Choose and document emission factors

An emission factor converts an activity into emissions: kilograms of CO2-equivalent per gallon of diesel, per kilowatt-hour, or per dollar of spend. Use EPA factors for direct fuels, EPA eGRID subregion factors for location-based electricity, and spend-based factors from an input-output model such as EPA USEEIO for the first pass at purchased goods. The rule that matters more than which library you pick: record the exact factor and its version for every line, so the number can be reproduced and restated next year.

5. Calculate Scope 1 from combustion records

Convert each fuel invoice to energy or physical quantity, apply the EPA factor, and add refrigerant leakage from service logs. This is your most direct and most audit-friendly data, because it comes from invoices with quantities on them. For most non-industrial companies Scope 1 is small; for manufacturers, construction firms and carriers it is a real chunk, and it is where assurance providers look first because it is the easiest to verify.

6. Calculate Scope 2 from electricity, both ways

Sum the kilowatt-hours from your utility bills per site and apply the grid factor for the location-based number. If you buy renewable energy through contracts, certificates or a green tariff, also calculate a market-based number that reflects those instruments. The GHG Protocol requires both. The difference between the two figures is exactly where your clean-power purchases show up, which is why we cover the two methods in detail in location-based vs market-based Scope 2.

7. Screen Scope 3 from spend

Classify your accounts payable file into categories and apply spend-based factors to get a complete first estimate across all fifteen categories at once. This is a screen, not a final answer: it tells you which two or three categories dominate, usually purchased goods, so you know where deeper data is worth collecting. The full procedure is in how to calculate Scope 3 from spend.

Scope	Primary data source	Factor type
Scope 1	Fuel and refrigerant invoices, meter reads	EPA fuel and gas factors
Scope 2	Utility bills (kWh), clean-power contracts	eGRID location-based and market-based
Scope 3	Accounts payable spend, then activity data on hotspots	Spend-based (USEEIO), then supplier-specific

8. Graduate the hotspots to activity data

Once the spend screen has ranked your Scope 3 categories, replace the estimates on your biggest lines with activity or supplier-specific data. Do not do this everywhere; do it only where a category is large enough that the precision changes a decision or survives a challenge. Everything in the long tail can stay spend-based until it grows or a customer asks about it.

9. Quality-check the numbers

Before anyone sees the figure, sanity-check it. Compare emissions per dollar of revenue against peers in your sector, look for sites with suspiciously low or high intensity, and confirm no source was double-counted or missed. A number that is an order of magnitude off usually means a unit error or a missing facility, and catching it now is far cheaper than explaining it during assurance.

10. Document the method and prepare for assurance

Write down your boundary, the sources you included, the factors and versions you used, and any estimates or exclusions with a reason. Assurance providers do not demand perfect data; they demand a method that is documented, consistent and proportionate, with every figure traceable to a source. If you keep the invoice behind each line attached from the start, the assurance sample is a lookup rather than a scramble.

Turning the checklist into a repeatable inventory

This checklist describes exactly how our carbon accounting software is built to work. It classifies your accounts payable and utility exports into scopes and categories, drafts an emission factor for every line with a confidence level, and keeps the source document attached to each figure, so the documentation trail in step ten is a by-product of the calculation rather than a separate project. If your reporting trigger is California, the same inventory feeds SB 253 reporting software directly. You can run the classification on your own lines in the demo, before any email address changes hands, and see where your hotspots sit.