How is annual commute CO2 calculated?

The tool multiplies your round-trip distance by the per-kilometre emission factor for your vehicle, then by the number of commuting days per year (days per week times the working weeks you set). The result is annual CO2e in kilograms.

Why does an electric car still show some emissions?

An EV produces no tailpipe CO2, but charging it draws electricity that usually carries some grid carbon. The tool applies a grid-based factor per kilometre, so the EV figure reflects how clean your electricity is. On a fully renewable tariff it approaches zero.

What emission factors does this use?

It uses representative UK DEFRA average-car factors: around 0.17 kgCO2e per km for an average petrol car, 0.16 for diesel, 0.12 for a hybrid, and roughly 0.05 for an EV on the average grid. Larger vehicles scale these up.

How do bus and train compare?

Public transport spreads emissions across many passengers, so per-passenger-kilometre figures are far lower: roughly 0.10 for a local bus and 0.035 for a national rail journey. Cycling and walking are effectively zero for the journey itself.

How many commuting days should I assume per year?

A typical full-time pattern is about 46 working weeks after holidays. At five days a week that is 230 commuting days. The tool lets you set weeks and days so you can model hybrid working, for example three office days a week.

Car Commute Carbon Calculator

Your commute can be the largest single line in your personal carbon footprint, and the gap between driving alone and taking the train is enormous. This calculator turns your distance, frequency, and vehicle into an annual CO2e figure using UK DEFRA factors, and compares it against public transport, cycling, and walking for the same trip.

How it works

round trip km = one-way km × 2
days per year = days per week × working weeks
annual CO2e   = round trip km × factor (kg/km) × days per year

The factor depends on fuel and size. The same journey is then re-costed against the per-passenger factors for bus and rail so you can see the saving from switching mode.

Emission factors used (kgCO2e per km)

Petrol average car: 0.170 · Diesel: 0.160 · Hybrid: 0.120 · EV (avg grid): 0.050
Size adjustment: small ×0.85, medium ×1.0, large/SUV ×1.30
Local bus: 0.100 · National rail: 0.035 · Cycling: 0 · Walking: 0

Notes

The EV figure scales with how clean your electricity is — on a renewable tariff it falls toward zero. Hybrid working has a large effect: dropping from five to three office days cuts commute emissions by 40 percent, which is often the single easiest reduction available.