Why do two carbon reports for the same factory and year show different totals?

Two reports for the same factory and year usually differ because they drew different boundaries, used different factor versions, chose different Scope 3 methods, or counted different gases. Line them up by scope, then by source, and the gap almost always traces to three or four lines.

The usual causes

1. Scope 3 method: one report multiplies tonnes of material by a material factor, the other multiplies rupee spend by an economic factor. This alone can move Scope 3 by a large share.
2. Scope 3 coverage: one report includes only purchased goods, the other adds freight, waste and business travel.
3. Boundary: one includes a leased warehouse, a second plant or contractor diesel used on site; the other does not.
4. Factor versions: different editions of the CEA grid database, or an international grid factor in place of the Indian one.
5. Scope 2 basis: location-based in one, market-based with RECs or a green tariff in the other.
6. Gases and GWP: CO2 only for fuels in one, CO2e with refrigerant leaks at AR5 or AR6 values in the other.
7. Period: April to March in one, January to December in the other.

How to find the gap in an afternoon

1. Put both reports side by side and compare Scope 1, Scope 2 and Scope 3 separately. The gap usually sits in one scope.
2. Within that scope, compare activity quantities first: litres, kWh, tonnes. If quantities differ, it is a boundary or data issue.
3. If quantities match, compare factors and their sources. If factors differ, it is a method or version issue.
4. Ask both preparers for the line items behind the scope that differs.

Which figure to use

Neither is right by default. Use the one whose boundary matches what you were asked for, whose factors are named and current, and whose quantities trace to documents. If a buyer prescribes a method or factor set, use that and keep the other report's working as a reconciliation note.

How this differs from a Scope 3 tool gap

When only the Scope 3 figures differ, the cause is nearly always method and category mapping. When Scope 1 or 2 differ too, look first at boundary and factor versions, because the underlying fuel and electricity quantities should be the same in both reports.

Illustrative example: one factory, two reports, a 28% gap

• Diesel in both: 20,000 L x 2.68 kg CO2/L = 53.6 t CO2
• Report A electricity: 300,000 kWh x 0.710 (CEA v21.0) = 213.0 t CO2
• Report B electricity: 300,000 kWh x 0.80 (assumed older factor, illustrative) = 240.0 t CO2
• Report A steel: 200 t x 2.0 t CO2e/t (assumed material factor) = 400 t CO2e
• Report B steel: Rs 1.6 crore x 0.035 kg CO2e per rupee (assumed spend factor) = 560 t CO2e
• Report A total: 53.6 + 213.0 + 400 = 666.6 t; Report B total: 53.6 + 240.0 + 560 = 853.6 t
• Gap: 187.0 t, so Report B is about 28% higher; the steel method causes 160 t of it

The 0.80 grid factor, the steel factor and the spend factor are assumptions chosen to show the mechanics, not published values.

What Senseible does here

Senseible pins the factor and its source to each line, which lets you compare its figures with another report line by line. Spend-based Scope 3 estimates are labelled as spend-based with wider uncertainty, so they are not mistaken for activity-based figures.

• Why two tools give different Scope 3
• AR5 or AR6 GWP: which to use
• Which CEA factor version for which year

Sources: GHG Protocol Corporate Standard, Chapters 3 and 4 (organisational and operational boundaries), GHG Protocol Scope 2 Guidance (location-based and market-based), CEA CO2 Baseline Database

Last reviewed 2026-10-18.