Carbon Footprint of a Car: Petrol vs Electric Comparison

Overview

Understanding the carbon footprint of a car is no longer just a task for environmental scientists; it is a vital part of being a responsible consumer in the UK today. As the UK government pushes toward a ban on the sale of new petrol and diesel cars by 2035, many of us are questioning the true environmental cost of our journeys. Whether you are commuting into London, driving the school run in Birmingham, or navigating the Highlands, every mile you cover adds to your personal greenhouse gas tally.

The carbon footprint of a car refers to the total amount of greenhouse gases—primarily carbon dioxide (CO2), but also methane (CH4) and nitrous oxide (N2O)—emitted during the vehicle's entire life cycle. This includes the "well-to-tank" emissions (extracting and refining fuel), the "tank-to-wheel" emissions (tailpipe exhaust), and the "embodied carbon" (manufacturing and disposing of the car itself). In this guide, we will break down the numbers, compare different fuel types, and provide actionable steps to reduce your impact.

The Numbers: Comparing Petrol vs. Electric

To understand the carbon footprint of a car, we must distinguish between different types of drivetrains. In the UK, the average passenger vehicle emits significantly different amounts of CO2e (carbon dioxide equivalent) based on whether it runs on fossil fuels or electricity.

According to data from the UK Department for Business, Energy & Industrial Strategy (BEIS) and DEFRA, the average medium-sized petrol car emits approximately 170g to 200g of CO2e per km when accounting for both fuel combustion and fuel supply chain (well-to-wheel). In contrast, an equivalent Battery Electric Vehicle (BEV) charged on the current UK National Grid emits roughly 40g to 50g of CO2e per km.

Life Cycle Comparison (60,000 miles)

If we look at a lifecycle of 60,000 miles (roughly 100,000 km), a typical petrol car will emit approximately 19,000 kg (19 tonnes) of CO2e through fuel alone. A battery-electric vehicle, even when accounting for the higher carbon intensity of manufacturing its battery, will emit roughly 5,000 kg (5 tonnes) of CO2e from electricity usage over that same distance. The "break-even" point—where the EV becomes cleaner than the petrol car—usually occurs within the first 15,000 to 20,000 miles of driving in the UK.

Why the Difference in Carbon Footprint of a Car?

The stark contrast between petrol and electric vehicles comes down to three main factors: energy efficiency, fuel source, and manufacturing intensity.

1. Thermodynamic Efficiency

Internal combustion engine (ICE) cars are remarkably inefficient. Approximately 70% to 80% of the energy stored in petrol is wasted as heat rather than moving the wheels. Electric motors, by comparison, are over 85-90% efficient. This means that even if the electricity came from "dirty" sources, the EV would often still pull ahead simply by using less raw energy to move the same distance.

2. The UK Grid Mix

The carbon footprint of a car that runs on electricity is directly tied to how that electricity is made. In the UK, we have seen a massive decarbonisation of the grid. In 2023, fossil fuels accounted for just over 30% of the UK’s electricity generation, with renewables and nuclear making up the rest. This makes a UK-based EV significantly cleaner than one driven in a country still heavily reliant on coal, such as Poland or parts of the US.

3. Embodied Carbon (The Manufacturing Debt)

It is important to acknowledge that the initial carbon footprint of a car is higher for an EV. Building a 60kWh lithium-ion battery is an energy-intensive process requiring mining for lithium, cobalt, and nickel. Estimates suggest that producing an EV generates about 30% to 40% more CO2 during the manufacturing phase than an ICE car. However, this "carbon debt" is paid back relatively quickly through lower operational emissions.

How to Calculate Carbon Footprint of a Car

If you want to know how to calculate carbon footprint of a car, you need to look at three variables: mileage, fuel consumption, and the fuel’s emission factor.

The basic formula is: Annual Mileage × (1 / Fuel Economy) × Fuel Emission Factor = Total Annual Emissions

In the UK, the standard conversion factors provided by the government are:

• Petrol: ~2.16 kg CO2e per litre.
• Diesel: ~2.56 kg CO2e per litre.
• Electricity: ~0.21 kg CO2e per kWh (this fluctuates based on grid performance).

For example, if you drive 8,000 miles a year in a petrol car that averages 40 mpg (roughly 14 km per litre), you are consuming approximately 920 litres of fuel. Multiplying 920 litres by 2.16 kg/litre gives you a direct tailpipe footprint of 1,987 kg of CO2e per year.

Reducing the Carbon Footprint of Driving a Car

Even if you aren't ready to switch to an electric vehicle, there are several ways to reduce the carbon footprint of driving a car.

• Eco-Driving Techniques: Smooth acceleration and braking can improve fuel efficiency by up to 15%. Maintaining a steady speed and avoiding excessive idling are simple but effective measures.
• Tyre Pressure: Under-inflated tyres increase rolling resistance, forcing the engine to work harder and burn more fuel. Check your pressures monthly.
• Weight and Aerodynamics: Remove roof racks when not in use and clear out heavy items from the boot. Every extra 50kg reduces your fuel economy by about 1-2%.
• Car-Sharing and Public Transport: The most effective way to reduce the carbon footprint of a car is to use it less. In the UK, the average car occupancy is just 1.5 people. By carpooling or using the rail network for long-distance trips, you drastically reduce your per-passenger-km emissions.

Bottom Line

The carbon footprint of a car is a complex metric that depends on what you drive, how you drive, and how much you drive. While no car is truly "zero-emission" when considering the full manufacturing lifecycle, the data clearly shows that in the UK, electric vehicles are the most effective way to reduce road transport emissions.

With a petrol vehicle emitting roughly 192g per km and an EV emitting roughly 43g per km (well-to-wheel), the transition to electric is essential for meeting the UK’s Net Zero targets. However, for those currently driving ICE vehicles, maintenance, eco-driving, and mileage reduction remain powerful tools for immediate climate action.

Ready to see exactly how your vehicle stacks up? Use our tool to calculate your footprint and discover tailored ways to offset or reduce your impact today.