Petrol vs Electric Calculator
The running cost per mile of a combustion car against an electric one, on your own prices.
The running cost of a car comes down to two numbers: how much energy it uses per mile, and what that energy costs you. Comparing a petrol car with an electric one is therefore a comparison of consumption and price, not of the cars themselves.
Enter both consumption figures and both prices, and this calculator shows the cost per mile and per year for each, the saving, and the electricity price at which the advantage disappears.
At a glance
- What you enter
- Miles driven per year, Petrol consumption (miles per gallon), Price per gallon, Electric consumption (kWh per 100 miles), Price per kWh of electricity, Charging efficiency
- What you get
- Petrol cost per mile, Electric cost per mile, Saving per year, Petrol cost per year, Electric cost per year
- Formula shown
- Yes - every step, right below your results.
- Cost and privacy
- Free, no account needed, and nothing you type is stored.
See worked examples ↓ Read the FAQ ↓ Share this calculator ↓
Results are estimates for general information only - always verify with a professional or official source before acting on them.
How to use the Petrol vs Electric Calculator
- 1 Enter Miles driven per year (miles)
- 2 Enter Petrol consumption (miles per gallon)
- 3 Enter Price per gallon
- 4 Enter Electric consumption (kWh per 100 miles)
- 5 Enter Price per kWh of electricity
- 6 Enter Charging efficiency
- 7 Press Calculate. You get Petrol cost per mile, Electric cost per mile, Saving per year, Petrol cost per year, Electric cost per year, and every intermediate step stays visible under “How is this calculated?”
- 8 Change one number at a time to see what moves the result - that is usually the most useful thing a calculator can tell you.
Worked examples
Real numbers run through this calculator. Open any example to load it into the form above and change it.
Home charging at $0.14 a kilowatt hour
A 12,000 mile year in a 32 mpg petrol car against an electric car charged at home.
You enter
- Miles driven per year
- 12,000 miles
- Petrol consumption (miles per gallon)
- 32
- Price per gallon
- $3.50
- Electric consumption (kWh per 100 miles)
- 17
- Price per kWh of electricity
- $0.14
- Charging efficiency
- 90%
You get
- Petrol cost per mile
- 0.11 per mile
- Electric cost per mile
- 0.03 per mile
- Saving per year
- $995.17
- Petrol cost per year
- $1,312.50
- Electric cost per year
- $317.33
Petrol costs $0.11 a mile and electricity $0.03, so the electric car is $0.08 a mile cheaper and $995.17 cheaper over 12,000 miles. The year costs $1,312.50 on petrol against $317.33 on electricity, so electricity is 24.2% of the petrol cost. The break-even electricity price is $0.58 a kilowatt hour against the $0.14 entered, and the car draws about 2,267 kWh from the supply over the year. Fuel is all that is counted here: servicing, tyres, insurance and depreciation are not in these figures.
Public rapid charging at $0.48 a kilowatt hour
A 9,000 mile year for a driver with no home charger, using the price of rapid chargers on the route.
You enter
- Miles driven per year
- 9,000 miles
- Petrol consumption (miles per gallon)
- 42
- Price per gallon
- $4.10
- Electric consumption (kWh per 100 miles)
- 20
- Price per kWh of electricity
- $0.48
- Charging efficiency
- 88%
You get
- Petrol cost per mile
- 0.10 per mile
- Electric cost per mile
- 0.11 per mile
- Saving per year
- -$103.25
- Petrol cost per year
- $878.57
- Electric cost per year
- $981.82
Petrol costs $0.10 a mile and electricity $0.11, so the electric car costs $0.01 a mile more and $103.25 more over the year: $878.57 on petrol against $981.82 on electricity. Electricity works out at 111.8% of the petrol cost, and the break-even price is $0.43 a kilowatt hour, below the $0.48 entered. The car uses only 2,045 kWh for the year, so this is a price problem rather than a consumption one: at the $0.14 domestic price from the first example, the same 9,000 miles would cost $286.36 in electricity.
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Frequently asked questions
Which electricity price should I enter?
The one you actually charge on. The electric cost per mile is the consumption divided by the charging efficiency and multiplied by the price, so a domestic overnight tariff and a public rapid charger give very different answers. In the second example $0.48 a kilowatt hour makes the electric car more expensive to run than the petrol one, even though it uses less energy for the same distance.
If most charging happens at home overnight, use the overnight rate. If most of it happens on the road, use what the chargers on your regular routes charge. Blending the two into one average is what makes the estimate unreliable.
What does charging efficiency mean?
It is the share of the electricity drawn from the supply that reaches the battery. Some energy is lost as heat in the charger, the cable and the battery itself, so 17 kWh per 100 miles at 90% efficiency draws about 18.9 kWh from the grid for the same distance. Entering 100 removes those losses from the calculation entirely, which flatters the electric car.
Cold weather, rapid charging and heating the cabin all make the real figure worse. A winter consumption figure from the car display is a better entry than a published one.
What is the break-even electricity price?
It is the price per kilowatt hour at which the two cars cost the same per mile: the petrol cost per mile divided by the electricity used per mile. It moves whenever the petrol price or either consumption figure changes. With petrol at $3.50 a gallon and 32 miles per gallon the break-even is $0.58, which is far above the $0.14 entered in the first example.
It is the number to check before assuming home tariffs apply. Compare it with what the rapid chargers on your regular routes actually charge, because that is the price that decides the answer for anyone without a driveway.
What is left out of this comparison?
Only energy is counted. Servicing, tyres, insurance, road tax and depreciation are all outside the figures, and between two particular cars they can outweigh the fuel difference by a wide margin. The Total Cost of Ownership Calculator is the page that adds them together over several years.
The purchase price is not here either, so an electric car that costs $1,000 a year less to run can still be the more expensive car overall if it costs $8,000 more to buy. Compare the annual difference with the price difference before deciding.