Quick verdict
For day-to-day energy cost alone, an electric car charged at home is usually the cheapest per mile. Diesel can still beat petrol for long motorway mileage if the car is efficient, but diesel’s pump price can wipe out some of that advantage.
Petrol at 40 MPG works out at about 17.7p per mile, diesel at 50 MPG about 16.1p per mile, and an EV charged at home at 3.5 miles/kWh about 7.5p per mile.
That does not mean electric is always cheapest overall. Insurance, depreciation, finance, charging access and purchase price can change the real winner.
Compare your own journey cost
Use your real distance, MPG, miles per kWh and local prices instead of relying on averages.
Petrol, diesel and electric cost per mile compared
The table below uses recent UK average fuel prices and Ofgem electricity assumptions. It is a comparison, not a guarantee, because local pump prices and charging tariffs vary.
| Vehicle / charging type | Example assumption | Energy price used | Approx. cost per mile | 10,000 miles/year |
|---|---|---|---|---|
| Petrol | 40 MPG | 155.54p/litre | 17.7p | £1,768 |
| Diesel | 50 MPG | 176.71p/litre | 16.1p | £1,607 |
| Electric — home charging | 3.5 miles/kWh | 26.11p/kWh | 7.5p | £746 |
| Electric — public charging | 3.5 miles/kWh | 54p/kWh | 15.4p | £1,543 |
The important lesson is that EVs look very different depending on charging access. A home charger on a sensible tariff can be much cheaper than petrol or diesel. Frequent public charging can make the gap much smaller.
How the cost per mile is calculated
Petrol and diesel cars are usually compared using MPG, while electric cars are compared using miles per kWh. That means the formulas are different.
Petrol and diesel formula
cost per mile = fuel price per litre × 4.54609 ÷ MPGThe 4.54609 figure is needed because UK MPG uses UK gallons, but petrol and diesel are sold by the litre.
Electric formula
cost per mile = electricity price per kWh ÷ miles per kWhFor a fuller charge calculation, including battery size, charging losses and target charge level, use the EV charging cost calculator.
When petrol can still make sense
Petrol is rarely the cheapest energy cost per mile, but it can still make sense if you drive low annual mileage, buy a cheaper used car, or mainly need a simple car for short local trips.
When diesel can still be cheaper than petrol
Diesel can work well for high-mileage motorway driving because efficient diesel cars often achieve better fuel economy than petrol equivalents. But the maths depends heavily on the diesel price and the type of driving.
Diesel is less attractive if most journeys are short, urban or stop-start. In that type of use, fuel economy can fall and maintenance risk can rise.
Use the MPG calculator to compare real fill-up MPG instead of relying only on advertised figures.
When electric is clearly cheaper per mile
Electric cars usually win the energy-cost calculation when you can charge at home. The example above uses 26.11p/kWh, but some EV-specific tariffs can be lower overnight, which can reduce the cost per mile further.
Electric is strongest when you do regular mileage, have off-street charging, and keep the car long enough for the lower running costs to matter. It is weaker when you rely heavily on expensive public rapid charging.
Working out charging cost?
Estimate charge cost, miles added, cost per mile and charging loss using your own battery and tariff.
Low mileage vs high mileage: the decision changes
The more miles you drive, the more important energy cost becomes. For low annual mileage, the difference between 8p and 17p per mile may not be enough to justify changing car. For high annual mileage, it can become a serious yearly saving.
| Annual mileage | Petrol at 17.7p/mile | Diesel at 16.1p/mile | EV home at 7.5p/mile |
|---|---|---|---|
| 5,000 miles | £884 | £803 | £373 |
| 10,000 miles | £1,768 | £1,607 | £746 |
| 15,000 miles | £2,652 | £2,410 | £1,119 |
This is why the same answer does not fit everyone. A city driver, motorway commuter and occasional weekend driver can all reach different conclusions.
Business mileage is a separate calculation
If you use your own vehicle for work journeys, the cheapest fuel type is not the same question as what you can claim. HMRC-approved mileage payments use fixed rates, not your exact fuel bill.
Use the mileage reimbursement calculator if you want to compare employer reimbursement with approved mileage amounts. The related term is approved mileage allowance payment.
FAQs
Is electric always cheaper than petrol or diesel?
No. Electric is usually cheaper per mile when charged at home, but public rapid charging, insurance, depreciation and purchase price can change the overall cost.
Is diesel cheaper than petrol per mile?
Often, but not always. Diesel cars can be more efficient, but diesel normally costs more per litre, so the real answer depends on MPG and pump price.
What is a good petrol cost per mile?
It depends on the car and fuel price, but a 40 MPG petrol car at around 155p/litre is roughly 17–18p per mile before parking, tax, insurance and maintenance.
What is a good EV cost per mile?
At 3.5 miles per kWh and 26.11p/kWh, the energy cost is about 7.5p per mile. Cheaper overnight tariffs can reduce this, while public charging can increase it.
Should I switch to electric just to save fuel?
Not without checking the full ownership cost. Compare energy savings with purchase price, finance, depreciation, insurance and charging access first.
Figures and sources to check
The examples on this page use rounded figures and should be updated when fuel, electricity or charging prices change.
- UK Fuel Price Index — weekly average unleaded and diesel prices.
- Ofgem price cap unit rates — average electricity unit-rate assumptions.
- GOV.UK advisory fuel rates — advisory petrol, diesel and electric rates for company-car fuel reimbursement.