Step 6: Calculate your emissions

This is step 6 of 7 in Build your GHG inventory. Previous: Step 5: Collect activity data. Next: Step 7: Report and verify.

Most companies calculate emissions with one formula: activity data multiplied by an emission factor. The hard part is not the arithmetic. It is choosing the right factor and keeping units consistent.

The formula

Emissions = activity data × emission factor

Activity data is the amount of the activity, from step 5.
An emission factor gives the emissions per unit of activity, for example kg CO₂e per kWh.

Some factors give each gas separately (CO₂, CH₄ and N₂O). Multiply each gas by its global warming potential (GWP), then add them up. IFRS S2 requires 100-year GWPs from the latest IPCC assessment, which is currently the Sixth Assessment Report (AR6).

Direct measurement, for example with a continuous emissions monitoring system on a chimney, is also allowed. Few companies outside heavy industry use it.

Where to find emission factors

Source	Use it for
Energy Commission of Malaysia (Suruhanjaya Tenaga), grid emission factors	Electricity from the Malaysian grids
Your supplier	Supplier-specific factors, for example a district cooling provider
UK DESNZ conversion factors (updated each year)	Fuels, vehicles, travel and waste, when no local factor exists
IPCC 2006 Guidelines	Default factors for fuels and processes

Malaysia does not yet publish its own factors for burning liquid and gaseous fuels. The Malaysian Green Technology and Climate Change Corporation (MGTC) uses the UK DESNZ factors for these in its own calculator.

Whichever source you use, record its name, edition and year. Use the same source each year for the same activity, unless a better factor becomes available. If you change, explain the change.

Worked examples

Electricity (Scope 2, location-based)

Malaysia has 3 grids with different factors. The Energy Commission's 2024 factors (provisional, published February 2026) are:

Grid	kg CO₂e per kWh
Peninsular Malaysia	0.740
Sabah	0.539
Sarawak	0.199

An office in Kuala Lumpur uses 10,000 kWh in a month:

10,000 kWh × 0.740 kg CO₂e/kWh = 7,400 kg CO₂e = 7.4 tCO₂e

The same office in Kuching would cause 1.99 tCO₂e, because Sarawak's grid uses mostly hydropower. Use the factor for the grid where each site is.

Diesel (Scope 1)

A delivery lorry uses 500 litres of diesel. With the UK DESNZ 2025 factor of 2.57082 kg CO₂e per litre (average biofuel blend):

500 litres × 2.57082 kg CO₂e/litre = 1,285 kg CO₂e = 1.29 tCO₂e

The DESNZ factors reflect the biofuel share of UK diesel and use AR5 GWPs for methane and nitrous oxide. Malaysian diesel has a different biodiesel blend. Record these differences as assumptions in your method notes.

Refrigerant leak (Scope 1)

A technician adds 2 kg of R-410A to an air conditioner during servicing. R-410A is a mix of 50% HFC-32 (GWP 771) and 50% HFC-125 (GWP 3,740), so its AR6 GWP is about 2,256:

2 kg × 2,256 = 4,512 kg CO₂e = 4.5 tCO₂e

This small leak causes more emissions than the 500 litres of diesel.

Market-based Scope 2

The market-based method uses the factors in your energy contracts. If renewable energy certificates (RECs) or a green tariff cover part of your electricity, that part has the factor in the contract. The rest uses a residual mix factor where one is published. If none is published, the GHG Protocol allows the grid average. IFRS S2 requires the location-based figure in all cases, so calculate both.

Special cases

Biogenic CO₂. CO₂ from burning biomass, such as wood or palm kernel shells, is reported separately from the 3 scopes. The CH₄ and N₂O from burning it stay in Scope 1.
Carbon credits. Do not subtract them from your emissions. Report them separately.
Units. Convert to one unit before you multiply. A factor in kg CO₂e per kWh needs kWh, not MWh.

Check the results

Compare each source with the previous period and with similar sites. Investigate large changes. Check the 3 largest sources by hand. Ask a second person to review the factors and the units.

Check your progress

Before you go to step 7, make sure that you have:

Emissions in tCO₂e for every source
A record of every emission factor and GWP, with its source and year
Location-based Scope 2, and market-based Scope 2 if you hold contracts

In Carbon GPT

When you record a measure in Measures, Carbon GPT applies the emission factor of its predefined measure and calculates the tCO₂e. Check the factor in each predefined measure before you start.

Sources

Step 7: Report and verify