What Is Your Car’s Real Carbon Per Mile?

Carbon per mile is the fairest and most meaningful way to compare petrol, diesel and electric vehicles. Here’s how to calculate it and why it matters.

By CarbonFree Team. Published 2025-11-07. Last updated 2026-10-21.

What Is Your Car’s Real Carbon Per Mile?

When we talk about vehicle emissions, it is easy to focus on claims like zero tailpipe or ULEZ compliant. But for climate impact, the metric that truly matters is grams of CO₂ per mile. This gives a single, comparable measure across petrol, diesel and electric vehicles.

Understanding this number helps you compare technologies, choose when to charge an EV and make clearer decisions about upgrades and finance.

Vehicle Emissions in Context

Carbon per mile reveals the real environmental impact of how you travel. It also shows how driving style and charging decisions influence emissions.

At CarbonFree Finance, we use carbon per mile to connect energy choices, emissions and long-term savings because lower-carbon behaviour often reduces household costs too.

Petrol and Diesel: Fixed Carbon from Fuel

For petrol and diesel vehicles, calculating carbon per mile is straightforward because burning fuel directly releases CO₂.

A litre of petrol emits around 2.3 kg of CO₂.

A litre of diesel emits around 2.7 kg of CO₂.

To estimate grams of CO₂ per mile:

  1. Look up the vehicle’s fuel economy (for example, 40 miles per gallon).
  2. Convert this to litres per mile (1 UK gallon is 4.546 litres):

40 mpg becomes 4.546 ÷ 40 = 0.114 L/mile.

  1. Multiply by the CO₂ per litre:

0.114 × 2.3 ≈ 0.26 kg/mile or around 260 g CO₂/mile.

A typical petrol car produces around 250 to 300 g CO₂ per mile. Diesel engines are more efficient, especially on long motorway journeys, and tend to fall slightly lower. However, diesel vehicles often produce more local air pollutants, so CO₂ is only part of the full environmental impact.

Electric Vehicles: Clean but Variable

Electric vehicles have no tailpipe emissions, but they do rely on electricity. The carbon intensity of this electricity changes throughout the day depending on how the grid is generating power.

To calculate EV carbon per mile:

EV efficiency in kWh per mile multiplied by the grid carbon intensity in grams per kWh, divided by 1000 to convert to kilograms.

Example:

If the same car charges during a low-carbon period, such as a windy night at 80 g CO₂/kWh:

0.30 × 80 = 24 g CO₂/mile.

This variation is entirely driven by the timing of charging.

Typical Emissions in the UK

Most EVs produce a quarter or less of the carbon emissions of petrol cars on the current grid mix. Charging at the right times can reduce this even further.

Why Charging Time Changes Everything

Electricity generation in the UK swings hourly depending on weather, demand and renewable output.

Low-carbon periods include the middle of the night during high wind and midday in summer when solar output is strong. Grid carbon intensity can fall below 50 g CO₂/kWh during these times.

During peak winter evenings, when gas turbines fill the gap left by low renewable output, carbon intensity can exceed 300 g CO₂/kWh.

Because EVs are flexible, charging off-peak significantly lowers emissions and often reduces energy cost at the same time. Smart charging systems can automatically shift charging to cleaner hours.

Our free Navigator Lite tool can help you understand when electricity in your area is cleanest.

How to Calculate Your Own Carbon per Mile

You can estimate your EV’s carbon per mile using:

Comparing the result with the typical petrol car baseline of roughly 280 g/mile shows how effective clean charging can be. Values between 20 and 50 g/mile indicate very efficient, low-carbon driving.

What This Means for Future Policy

As the UK moves toward replacing fuel duty, carbon per mile is likely to become central to fair taxation. A system based on carbon rather than distance automatically rewards charging during clean periods and reflects the environmental goal directly.

This creates a simpler, more transparent link between personal energy behaviour and national emissions targets.

CarbonFree Finance integrates this thinking into energy modelling, finance planning and customer advice. Smarter charging, better home energy choices and the right financing can all work together to reduce emissions and monthly costs.

Key Takeaway

Petrol vehicles typically emit 250 to 300 g CO₂ per mile.

Diesel vehicles average 220 to 280 g CO₂ per mile.

Electric vehicles can range from 20 to 70 g CO₂ per mile depending on grid conditions.

Smart charging reduces both emissions and cost.

Carbon per mile is the most meaningful and fair way to compare vehicles and assess environmental impact.

---

Ready to take action?

Partners and installers: