How Much Does a Petrol Car Cost per Mile: What the Maths Says With Real Assumptions

The question behind how much does a petrol car cost per mile is really two smaller questions: what does each car use per mile, and what does that energy cost where you buy it. Answer those two and the comparison is arithmetic. This page answers them in order, states the assumptions openly, and then shows the result at several annual mileages so you can see how the answer scales. Where the page leaves something out — purchase price, depreciation, insurance, servicing and tax — it says so by name.

The short answer is that the comparison comes down to cost per mile: the petrol car burns US gallons, so its cost per mile is the price per gallon divided by its MPG, while the EV uses kilowatt-hours, so its cost per mile is the electricity price per kWh divided by its miles per kWh. With the example assumptions on this page — petrol at $3.45 per US gallon, 30 US MPG, electricity at 28 cents per kWh and 4.0 miles per kWh — the petrol car costs about $0.12 per mile and the EV about $0.07 per mile. Those are example figures, not prices you should quote, and the rest of this page shows how they were reached and what would change them.

Assumptions used on this page for how much does a petrol car cost per mile

Taking how much does a petrol car cost per mile as the case in point: Every figure in the tables below comes from this assumptions table. Each one is an assumption or an example, not a measured fact about any particular car or a current price. Substitute your own numbers and the method still works.

Input Value used Status
Petrol price $3.45 per US gallon Example price
Petrol efficiency 30 US MPG Assumption
Electricity price 28 cents per kWh Example price
EV efficiency 4.0 miles per kWh Assumption
Annual mileage 15,000 miles Example

how much does a petrol car cost per mile: How the EV versus petrol comparison works

Hold the mileage constant and price the energy each car actually uses. For the petrol car, cost per mile equals the price per gallon divided by its MPG. For the EV, cost per mile equals the price per kWh divided by its miles per kWh. Multiply each cost per mile by the annual mileage and you have the annual fuel and charging bill for each car; subtract one from the other and you have the saving, or the extra cost, under those assumptions. The method is deliberately simple, because a simple method with honest inputs beats a complicated model built on guessed ones. The two numbers that matter most are the electricity price and the petrol car's MPG: a driver who charges at home on a cheap overnight rate will see a very different answer from a driver who relies on public rapid chargers, and a thirsty petrol car widens the gap while an efficient one narrows it. That is the point this page works through for how much does a petrol car cost per mile.

Worked example: the same distance, two energy bills for how much does a petrol car cost per mile

Take a driver covering 15,000 miles a year. The petrol car does 30 MPG and petrol costs $3.45 per gallon as an example price, so its cost per mile is $3.45 ÷ 30 = $0.12, and 15,000 miles cost $1,725.00 a year. The EV does 4.0 miles per kWh and electricity costs 28 cents per kWh as an example price, so its cost per mile is $0.28 ÷ 4.0 = $0.07, and 15,000 miles cost $1,050.00 a year. The difference on fuel and charging alone is $675.00 a year in the EV’s favour under these assumptions. Now change one input and watch the answer move: if the EV is charged mostly at a public rapid charger at, say, double the home electricity price used here, its annual charging cost doubles and most of the saving disappears. If the petrol car is driven mainly in town at lower MPG, the petrol bill rises and the saving grows. That sensitivity is the real lesson — the answer is only as solid as the assumptions, so write yours down before you believe the result.

how much does a petrol car cost per mile: Cost at different annual mileages

The table uses the worked-example assumptions above — petrol at $3.45 per gallon (example), 30 MPG, electricity at 28 cents per kWh (example), 4.0 miles per kWh. The gap grows with mileage, which is why high-mileage drivers see the biggest fuel-cost difference and low-mileage drivers see the smallest.

Annual miles Petrol cost per year EV charging cost per year Difference
6,000 $690.00 $420.00 $270.00
8,000 $920.00 $560.00 $360.00
10,000 $1,150.00 $700.00 $450.00
12,000 $1,380.00 $840.00 $540.00
15,000 $1,725.00 $1,050.00 $675.00
20,000 $2,300.00 $1,400.00 $900.00

Cost per mile and per 100 miles for how much does a petrol car cost per mile

At the example assumptions, the petrol car costs $0.12 per mile ($11.50 per 100 miles) and the EV costs $0.07 per mile ($7.00 per 100 miles). Per 100 miles is often the easier figure to compare with a fuel receipt or a charging bill, because both are usually priced in round numbers per hundred miles of driving. If you know your own MPG and your own prices, the same two divisions give your own figures: fuel price per gallon divided by MPG, and electricity price per kWh divided by miles per kWh.

how much does a petrol car cost per mile: What the comparison leaves out — and why it matters

For how much does a petrol car cost per mile, the point is this: The fuel and charging maths on this page is only one slice of the real cost. Left out, by design, are the purchase-price gap between the two cars, depreciation, insurance, servicing, tyre wear and tax — every one of them differs between an EV and a petrol car and every one of them moves the true answer. The page also prices electricity at a single rate, while real life mixes cheap overnight home charging with dear public rapid charging; that mix usually matters more than the headline rate. Price your own mix honestly before deciding which car is cheaper for you.

Common mistakes for how much does a petrol car cost per mile

  • For how much does a petrol car cost per mile, the point is this: Using one tank or one charge instead of an average is next — a single fill is noisy, and a pump that clicks off early can add a phantom gallon, while a single charge says nothing about your usual mix of home and public charging.
  • On this page, how much does a petrol car cost per mile is the case in point: Comparing a laboratory test figure against a real-world figure tells you nothing about the car and everything about the methods. Keep the method constant — real-world against real-world — and the comparisons become meaningful.
  • For how much does a petrol car cost per mile, the point is this: Comparing a car's best-case efficiency with another's everyday figure is another trap. Brochure efficiency is measured in controlled conditions; your real miles per kWh or MPG will be lower, and the comparison only works when both cars are measured the same way.
  • For how much does a petrol car cost per mile, the point is this: Treating the example prices on this page as current prices is the last mistake. Fuel and electricity prices move constantly, so always substitute the prices you actually pay before trusting any saving.

Related calculations for how much does a petrol car cost per mile

For how much does a petrol car cost per mile, the point is this: If this page answered your question, these pages take the next step — the same method applied to a closely related question, or the calculator that does the arithmetic for you.

Putting your figure to work for how much does a petrol car cost per mile

On this page, how much does a petrol car cost per mile is the case in point: Use the result as a tool, not a verdict. Re-run the two divisions with your own prices and efficiencies whenever they change, and the comparison stays honest. A monthly log — miles, energy used, price paid — is enough to spot the patterns that matter: colder months cost more per mile for an EV, a new charging habit shifts the average, and a petrol car driven more in town drifts the other way. Measured figures beat remembered ones, and the method on this page is built for measured figures.

Frequently asked questions

Why do EV running-cost figures disagree so much?

Because the inputs differ. Two honest calculations can give very different answers if one assumes cheap home charging and the other assumes public rapid charging, or if one uses a high-mileage year and the other a low one. Always ask what electricity price, what MPG and what mileage a figure was calculated with before comparing it with another. That is the point this page works through for how much does a petrol car cost per mile.

Can I use the same method for a diesel car?

On this page, how much does a petrol car cost per mile is the case in point: Yes. A diesel car uses the same petrol-side formula — fuel price per gallon divided by MPG — with diesel prices and diesel MPG. The EV side is unchanged. Compare the two cost-per-mile figures the same way, and remember the same exclusions apply.

What does miles per kWh mean?

Taking how much does a petrol car cost per mile as the case in point: It is the EV equivalent of MPG: how many miles the car travels on one kilowatt-hour of electricity. Higher is more efficient. Divide the electricity price per kWh by miles per kWh to get the EV's cost per mile, in the same way you divide the fuel price per gallon by MPG for a petrol car.

Does an EV cost more to insure?

Taking how much does a petrol car cost per mile as the case in point: Insurance is not part of the fuel-and-charging maths on this page, and it can differ between an EV and a petrol car for reasons that have nothing to do with energy: repair costs, parts availability and the car's value all play a part. Get a quote for both cars before comparing total costs.

How many kWh does it take to charge an EV?

Taking how much does a petrol car cost per mile as the case in point: It depends on the battery size and how empty it is. A charge from near-empty to full takes roughly the battery's capacity in kWh, plus a few percent for charging losses. Divide the kWh drawn by the miles driven afterwards and you have the car's real miles per kWh for that period.