Why is the EV usually cheapest per mile?

An electric motor converts far more of its energy into motion than a combustion engine, and electricity is cheaper per unit of useful energy than petrol or diesel. Home-charged EVs often cost a third or less per mile of an equivalent petrol car.

How is cost per mile worked out?

For liquid fuels it is the price per litre divided by the miles travelled per litre (mpg converted to metric). For the EV it is the price per kWh divided by miles per kWh. Multiplying by your distance gives the total trip cost.

Where do the CO2 figures come from?

Tailpipe CO2 uses DEFRA factors per litre — about 2.31 kg for petrol, 2.51 for diesel, 1.51 for LPG — divided by miles per litre. The EV uses grid electricity carbon intensity per kWh, which varies by country and time of day.

What is the tax breakdown?

UK pump prices include fuel duty (a fixed pence per litre) plus VAT at 20 percent on the whole price including duty. The tool estimates how much of each mile's fuel cost is tax, which is far higher for petrol and diesel than for electricity.

Is grid electricity really zero carbon?

No. The EV's CO2 depends entirely on how the electricity was generated. On a renewable tariff it is very low; on a coal-heavy grid it can approach a small petrol car. The tool lets you set the grid intensity so the comparison reflects your real supply.

Fuel Cost vs CO2 Comparator

This comparator puts four fuels side by side — petrol, diesel, LPG, and electric — on the two metrics that matter for running costs and policy: cost per mile and CO2e per mile. You enter each vehicle’s efficiency, the relevant prices, and a distance, and it ranks them with a UK fuel-duty and VAT breakdown.

How it works

For liquid fuels, miles per gallon is converted to miles per litre, then cost and CO2 follow from price and emission factor per litre. The EV works from miles per kWh and the grid carbon intensity:

mpl          = mpg / 4.546                 (UK gallon = 4.546 L)
cost_per_mile = price_per_litre / mpl
co2_per_mile  = factor_per_litre / mpl
EV: cost_per_mile = price_per_kWh / miles_per_kWh
    co2_per_mile  = grid_factor / miles_per_kWh

DEFRA tailpipe factors are about 2.31 kg CO2 per litre of petrol, 2.51 for diesel, and 1.51 for LPG. The tax line splits the pump price into fuel duty plus 20 percent VAT charged on top of the duty-inclusive price.

Tips and example

A 45 mpg petrol car at 1.45 per litre costs about 14.6p per mile and emits roughly 234 g CO2 per mile, while an EV doing 3.5 miles per kWh charged at 0.10 per kWh costs under 3p per mile. Over a 10,000-mile year the EV saves well over a thousand in fuel. Remember the EV’s carbon depends on your grid mix, so set the intensity to match your real tariff before comparing emissions.