How to Calculate Natural Gas Emissions: Formula, Factor and Example

Natural gas is the largest direct emission source for many industrial facilities and office buildings in Türkiye. The calculation itself is simple; the problems usually arise in the units. The invoice shows Sm³, kWh and kcal together, while IPCC factors are given on a different energy basis. This guide walks through the path from invoice to tCO₂e, showing every step.

Why are natural gas emissions Scope 1?

The GHG Protocol Corporate Standard defines fuel combustion in sources the company owns or controls, such as boilers, furnaces and turbines, as direct emissions, i.e. Scope 1 (Chapter 4, pp. 25-27). In practice, the following items fall under Scope 1:

• Steam and hot water boilers, thermal oil boilers
• Heat treatment, drying and baking ovens
• Cogeneration and trigeneration engines
• Combi boilers and boilers for building heating
• Kitchen and canteen cookers

The boundary question is who controls the source. If the owner operates the central boiler of a building you lease, or if you buy steam from another company, the situation changes. For details, see the organizational and operational boundaries guide. Emissions from extracting, processing and transporting the gas by pipeline are not your Scope 1; they are reported separately in Scope 3 Category 3 (fuel- and energy-related activities).

Formula

The IPCC Tier 1 approach for stationary combustion is to convert the amount of fuel into an energy unit and multiply it by each gas's factor:

Emissions (kg CO₂e) = Fuel (TJ, net calorific value) × [EF_CO₂ + (EF_CH₄ × GWP_CH₄) + (EF_N₂O × GWP_N₂O)]

Here the EF values are in kg/TJ. Divide the result by 1,000 to get tCO₂e. The critical part of the formula is the first term: converting the fuel to TJ on the correct energy basis.

Units on the invoice: Sm³, kWh and kcal

In Türkiye, a natural gas invoice shows three pieces of information together:

• Sm³ (standard cubic metre): As defined by BOTAŞ (the Turkish state pipeline and gas trading company), a volume of 1 m³ of gas at 15 °C and 1.01325 bar absolute pressure. The meter reading is corrected to these conditions and written on the invoice.
• Gross calorific value (kcal/Sm³): The energy content of a unit volume of gas. For presentation on an energy basis, the billing communiqué takes a gross calorific value of 9,155 kcal/m³ and accepts 1 m³ = 10.64 kWh (Article 4). The actual value is the volume-flow-weighted average of the daily gross calorific values over the billing period (Article 3).
• kWh: The product of Sm³ and the actual gross calorific value. Because it reflects the gas's real energy content for that period, it is the most valuable line for the calculation.

Gross vs net calorific value

The "üst ısıl değer" on a Turkish invoice is the gross calorific value (GCV), also called the higher heating value. IPCC factors, however, are on a net calorific value (NCV) basis. The difference is the latent heat of the water vapour formed during combustion. According to the IPCC, the net calorific value of natural gas is about 10 percent lower than the gross calorific value; for coal and oil products the difference is about 5 percent (Volume 2, Chapter 1, p. 1.16). The UK government's 2026 factors show the same picture: for natural gas, the gross CV factor is 0.18231 and the net CV factor is 0.20199 kg CO₂e/kWh, a ratio of 0.903.

The result: if you multiply the kWh on the invoice directly by the IPCC's NCV-based factor, you will overstate emissions by about 10 percent. The correct approach is either to convert the kWh to net calorific value by multiplying it by 0.90, or to use a factor published on a gross calorific value basis.

Useful conversions:

• 1 kWh = 3.6 MJ = 0.0036 GJ
• 1 TJ = 1,000 GJ
• 1 kcal = 4.1868 kJ (Türkiye's inventory takes 1 tonne of oil equivalent as 41.868 GJ in its conversions)

Which factor: IPCC, Türkiye's national inventory or DESNZ

Türkiye's inventory uses a country-specific CO₂ factor for natural gas, and this value is about 1 percent lower than the IPCC default. Both options are defensible; what matters is justifying the choice, recording its year and staying consistent across years. For the general framework on factor selection, see our post on emission factor selection.

GWP: which IPCC report do we use?

Converting CH₄ and N₂O to CO₂ equivalent requires the global warming potential (GWP). In this guide's calculations we use IPCC AR6 values, because the GHG Protocol's GWP document dated August 2024 recommends AR6 as the most up-to-date values. The same document asks that methane from fuel combustion use the "non-fossil" methane GWP rather than the fossil one; since the CO₂ from combustion is already counted separately, the fossil value would lead to double counting. Accordingly:

• CH₄ (non-fossil, AR6): 27.0
• N₂O (AR6): 273

Türkiye's 2024 national inventory and DESNZ's 2026 fuel factors use AR5 (CH₄ 28, N₂O 265). For natural gas combustion this difference is negligible in practice: in the example below, the result changes by only about 9 kg CO₂e with AR5. If a programme you report to requires a specific GWP set, follow it, and always state which set you used.

Step-by-step example: a textile dyehouse

All consumption figures below are illustrative values. A dyehouse uses natural gas in its steam boilers and stenter machines. The following totals are taken from 12 months of distribution invoices for 2025:

• Total consumption: 1,250,000 Sm³
• Total energy on the invoices: 13,350,000 kWh (gross calorific value basis)

The average calorific value is 13,350,000 ÷ 1,250,000 = 10.68 kWh/Sm³, which is close to the communiqué's reference of 10.64 kWh.

Step 1, convert kWh to energy: 13,350,000 kWh × 0.0036 GJ/kWh = 48,060 GJ = 48.06 TJ (gross calorific value)

Step 2, move to net calorific value (IPCC, about 10 percent difference): 48.06 TJ × 0.90 = 43.254 TJ (net calorific value)

Step 3, CO₂ (IPCC Table 2.3, 56,100 kg/TJ): 43.254 × 56,100 = 2,426,549 kg = 2,426.55 t CO₂

Step 4, CH₄ (1 kg/TJ, GWP 27.0): 43.254 × 1 = 43.25 kg CH₄ → 43.25 × 27.0 = 1,168 kg = 1.17 t CO₂e

Step 5, N₂O (0.1 kg/TJ, GWP 273): 43.254 × 0.1 = 4.33 kg N₂O → 4.33 × 273 = 1,181 kg = 1.18 t CO₂e

Total: 2,426.55 + 1.17 + 1.18 = 2,428.90 tCO₂e

This means 2,428,898 ÷ 1,250,000 = 1.943 kg CO₂e per Sm³ for this facility's gas. CH₄ and N₂O make up about one-thousandth of the total.

Cross-check: the same facility with different factors

The first three results are within about 2 percent of each other. The last row is about 4 percent higher. The reason: the ratio of DESNZ's m³ and kWh factors (2.02633 ÷ 0.18231) corresponds to an energy content of about 11.11 kWh/m³ for UK gas, while the gas at the example facility is 10.68 kWh/Sm³. If you use a foreign dataset, choose its energy-based factor, not its volume-based one.

Calculators

If your invoice total is in Sm³, use the first calculator:

Using the kWh total on the invoice is more precise. Divide the kWh value by 1,000 and enter it in MWh:

Other stationary fuels: fuel oil, LPG and coal

The same logic applies to other fuels; only the factors and calorific values change. The table below is derived from IPCC 2006 defaults (Volume 2, Table 1.2 net calorific values, Table 2.3 manufacturing industry emission factors). The last column is CO₂ per tonne of fuel.

The lignite rows carry an important warning: in Türkiye's inventory, the average net calorific value of lignite for 2022 is 8.24 TJ/kt, while the IPCC default is 11.9. For the same tonne of lignite, the IPCC default gives about 39 percent more CO₂. For solid fuels, instead of a default per-tonne factor, use the net calorific value from the analysis report the supplier provides for each batch, and calculate on an energy basis. If you buy liquid fuel by the litre, take the density from the supplier's documents as well.

Common mistakes

1. Multiplying invoice kWh by an NCV-based factor. In Türkiye, the kWh on the invoice is on a gross calorific value basis. Multiplying it directly by the IPCC factor inflates emissions by about 10 percent.
2. Using a volume-based foreign factor. The UK's m³ factor is based on a different gas composition. In the example, this mistake raised the result by about 4 percent.
3. Confusing the invoice period with the calendar year. December consumption is often invoiced in January. Build the annual total from meter reading dates; if necessary, apportion the last period by number of days.
4. Double counting cogeneration. All the gas burned in cogeneration is Scope 1. Do not also record the electricity you generate and consume at the same site under Scope 2.
5. Using the same CH₄ factor for offices and factories. The IPCC gives 5 kg CH₄/TJ for commercial and institutional buildings and 1 kg/TJ for industry. The effect is small, but separate them for consistency.
6. Not recording the source and year. An inventory that does not state the factor's source, year, energy basis and GWP set in the calculation file will get its first verification question here.
7. Adding upstream emissions to Scope 1. Emissions from producing and transporting the gas are Scope 3 Category 3. Scope 1 includes only the gases released by your own combustion.

Keeping the data verification-ready

A verifier usually checks the invoices and meter records first, then the conversions in the calculation file. So keep the following in a single folder:

• 12 months of distribution invoices (with the Sm³, kWh and gross calorific value lines visible)
• If there are several meters, a list of meters and which building each one supplies
• If you allocate using sub-meters, a reconciliation of the sub-meter total with the main meter
• The source page and version of the factor table used

For the points most often checked in verification, see our post the first 10 things checked in emissions verification.

Next step

Natural gas is usually the largest part of Scope 1, but not its only item. To build the whole inventory, go back to the carbon footprint calculation guide; for electricity, continue with electricity emissions calculation, and for the vehicle fleet with company vehicle emissions calculation. If you want to turn your facility's fuel data into a verification-ready inventory, Alalëa's carbon footprint service takes this work from data collection to reporting together with you.