Co2 Calculations Explained

Vehicle emissions Factors

Each vehicle type emits a different amount of CO2 per kilometre, depending on factors like fuel type, engine efficiency, and use of electric power. These emissions factors are based on average values for real-world fuel consumption and CO2 emissions data sources from the UK Government Energy Report and the Carbon Trust.

Trees absorb CO2 from the atmosphere through the process of photosynthesis. On average, a mature tree absorbs approximately 22 kg of CO2 per year. This value is based on estimates from The European Environment Agency (EEA) & U.S. Environmental Protection Agency (EPA).

How We Calculate CO2 Emissions & Trees

For each vehicle type, the formula used to calculate CO2 emissions is:

CO2 Emissions (kg) = Distance (km) × Emission Factor (kg CO2/km)

The distance can be entered in either kilometres or miles. If entered in miles, we first convert the distance to kilometres:

Distance (km) = Distance (miles) × 1.60934

The formula for Trees Needed to Offset CO2 Emissions:

Trees Needed = CO2 Emissions (kg) ÷ 22

1. Diesel Vehicles

Emission Factor:

2.68 kg CO2/km

Diesel engines generally produce higher CO2 emissions than petrol due to the higher energy density of diesel fuel.

Formula:

CO2 Emissions = Distance (km) × 2.68

For a 100 km journey in a diesel vehicle:

CO2 Emissions = 100 × 2.68 = 268 kg CO2

Trees Needed = (Distance (km) × 2.68) ÷ 22

A 100 km diesel journey:

CO2 Emissions = 100 × 2.68 = 268 kg CO2
Trees Needed = 268 ÷ 22 = 12.18 (rounded to 12 trees)

2. Petrol (Gasoline) Vehicles

Emission Factor:

2.31 kg CO2/km

Petrol vehicles are less efficient than diesel but produce slightly lower CO2 emissions per kilometre.

Formula:

CO2 Emissions = Distance (km) × 2.31

For a 100 km journey in a petrol vehicle:

CO2 Emissions = 100 × 2.31 = 231 kg CO2

Trees Needed = (Distance (km) × 2.31) ÷ 22

A 100 km petrol journey:

CO2 Emissions = 231 kg CO2
Trees Needed = 231 ÷ 22 = 10.5 (rounded to 11 trees)

3. Mild Hybrid Vehicles

Emission Factor:

1.91 kg CO2/km

Mild hybrid vehicles combine a combustion engine with an electric motor, reducing CO2 emissions compared to traditional petrol or diesel engines.

Formula:

CO2 Emissions = Distance (km) × 1.91

For a 100 km journey in a mild hybrid vehicle:

CO2 Emissions = 100 × 1.91 = 191 kg CO2

Trees Needed = (Distance (km) × 1.91) ÷ 22

A 100 km mild hybrid journey:

CO2 Emissions = 191 kg CO2
Trees Needed = 191 ÷ 22 = 8.68 (rounded to 9 trees)

4. PHEV (Plug-in Hybrid Electric Vehicle)

Emission Factor:

1.37 kg CO2/km

PHEVs can run on electric power for short distances but use a combustion engine for longer trips, resulting in lower CO2 emissions compared to traditional engines. They can be charged via an external socket like an EV, hence the plug-in.

Formula:

CO2 Emissions = Distance (km) × 1.37

For a 100 km journey in a PHEV:

CO2 Emissions = 100 × 1.37 = 137 kg CO2

Trees Needed = (Distance (km) × 1.37) ÷ 22

A 100 km PHEV journey:

CO2 Emissions = 137 kg CO2
Trees Needed = 137 ÷ 22 = 6.23 (rounded to 6 trees)

5. Electric Vehicles (EVs)

Emission Factor:

0.233 kg CO2/km

Electric vehicles produce little to no direct CO2 emissions. However, emissions are generated during electricity production. In the UK, the average emission factor for EVs is 0.233 kg CO2/km, but this varies depending on the electricity mix of the grid in your location. You can check the greens of the grid here: National Grid Live.

Formula:

CO2 Emissions = Distance (km) × 0.233

For a 100 km journey in an EV:

CO2 Emissions = 100 × 0.233 = 23.3 kg CO2

Trees Needed = (Distance (km) × 0.233) ÷ 22

A 100 km EV journey:

CO2 Emissions = 23.3 kg CO2
Trees Needed = 23.3 ÷ 22 = 1.06 (rounded to 1 tree)

Sources

1. European Environment Agency (EEA) - Carbon capture by forests and soil: https://www.eea.europa.eu/
2. U.S. Environmental Protection Agency (EPA) - How much carbon dioxide does a tree absorb?: https://www.epa.gov/
3. UK Government - Department for Business, Energy & Industrial Strategy (BEIS): https://www.gov.uk/government/organisations/department-for-business-energy-and-industrial-strategy
4. Carbon Trust - Transport Emission Factors: https://www.carbontrust.com/