EV vs Petrol Calculator by Car: A Step-by-Step Worked Example

There is no single number that answers ev vs petrol calculator by car, because the answer moves with four inputs: the price of petrol, the petrol car's MPG, the price of electricity and the EV's miles per kWh. Change any one and the result changes, sometimes by enough to flip the conclusion. That is why this page shows its working instead of handing you a verdict: the formula, a worked example with stated assumptions, and tables at different mileages.

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 22 cents per kWh and 4.0 miles per kWh — the petrol car costs about $0.12 per mile and the EV about $0.06 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 ev vs petrol calculator by car

For ev vs petrol calculator by car, the point is this: 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 22 cents per kWh Example price
EV efficiency 4.0 miles per kWh Assumption
Annual mileage 10,000 miles Example

How the EV versus petrol comparison works for ev vs petrol calculator by car

Taking ev vs petrol calculator by car as the case in point: 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.

Worked example: the same distance, two energy bills for ev vs petrol calculator by car

Take a driver covering 10,000 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 10,000 miles cost $1,150.00 a year. The EV does 4.0 miles per kWh and electricity costs 22 cents per kWh as an example price, so its cost per mile is $0.22 ÷ 4.0 = $0.06, and 10,000 miles cost $550.00 a year. The difference on fuel and charging alone is $600.00 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.

Cost at different annual mileages for ev vs petrol calculator by car

The table uses the worked-example assumptions above — petrol at $3.45 per gallon (example), 30 MPG, electricity at 22 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 $330.00 $360.00
8,000 $920.00 $440.00 $480.00
10,000 $1,150.00 $550.00 $600.00
12,000 $1,380.00 $660.00 $720.00
15,000 $1,725.00 $825.00 $900.00
20,000 $2,300.00 $1,100.00 $1,200.00

Cost per mile and per 100 miles for ev vs petrol calculator by car

At the example assumptions, the petrol car costs $0.12 per mile ($11.50 per 100 miles) and the EV costs $0.06 per mile ($5.50 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.

Comparing by car or by mileage for ev vs petrol calculator by car

On this page, ev vs petrol calculator by car is the case in point: The only fair comparison holds the mileage constant and uses each car's own efficiency. Comparing two cars over different mileages, or comparing one car's best-case efficiency with another's worst case, tells you nothing. Pick a mileage you actually drive, use each car's realistic efficiency — not its brochure figure — and price the energy at the rate you actually pay. If you are comparing specific models, do the same sum for each one separately and compare the totals, rather than trusting a single headline saving that may have been calculated at a mileage you will never drive.

ev vs petrol calculator by car: What the comparison leaves out — and why it matters

For ev vs petrol calculator by car, 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.

ev vs petrol calculator by car: Common mistakes

  • 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. That is the point this page works through for ev vs petrol calculator by car.
  • Taking ev vs petrol calculator by car as the case in point: 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.
  • Using the same electricity price for every charge hides the real cost. A driver who mixes home and public charging has two different prices, and averaging them into one number without weighting by how much energy comes from each is a common error. That is the point this page works through for ev vs petrol calculator by car.
  • For ev vs petrol calculator by car, the point is this: Forgetting that winter changes EV efficiency is easy to miss. Cold weather reduces an EV's miles per kWh noticeably, so a saving calculated on summer figures will overstate the winter result.

Related calculations for ev vs petrol calculator by car

For the next step, these pages apply the same method to a closely related question — or hand the arithmetic to the calculator. That is the point this page works through for ev vs petrol calculator by car.

ev vs petrol calculator by car: Putting your figure to work

For ev vs petrol calculator by car, the point is this: The method earns its keep when you run it on your own numbers. Measure your real cost per mile for each car — your prices, your efficiency, your charging mix — and you can price a journey before you leave and compare two cars on equal terms instead of brochure claims. Keep a small log of date, miles, energy and price, and look at it monthly: a winter efficiency dip, a change in your charging mix and a slow cost creep all show up fast, and each one is something you can act on.

Frequently asked questions

What affects an EV's miles per kWh?

Driving speed, temperature, heating and air conditioning, tyre pressures and how much town versus motorway driving you do. Cold weather and high speeds reduce miles per kWh, while gentle town driving usually improves it. Measure yours over several weeks rather than trusting a single trip. That is the point this page works through for ev vs petrol calculator by car.

Can I use the same method for a diesel car?

Taking ev vs petrol calculator by car as 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.

How do I work out my own EV versus petrol saving?

For ev vs petrol calculator by car, the point is this: Use the same mileage for both cars. For the petrol car, divide the fuel price per gallon by its MPG to get cost per mile. For the EV, divide the electricity price per kWh by its miles per kWh. Multiply each by your annual miles and subtract. Use your own prices — especially your real charging mix of home and public charging — rather than the example prices on this page.

How sensitive is the saving to the electricity price?

For ev vs petrol calculator by car, the point is this: Very sensitive. Doubling the electricity price doubles the EV's charging cost per mile, while the petrol side is unchanged. That is why this page states its example prices openly: change the electricity price to the one you actually pay and the saving changes with it, sometimes by enough to change the conclusion.

How many kWh does it take to charge an EV?

For ev vs petrol calculator by car, the point is this: 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.