EV vs Petrol Which Is Better for Me: Formula, Tables and What Is Left Out

If you want a straight answer on ev vs petrol which is better for me, start with the maths, not a headline figure. This page works through the formula step by step, runs a worked example with every assumption stated in full, and gives you tables you can read your own numbers off. Nothing here is presented as a current price or a measured efficiency: every figure is labelled as an assumption or an example, and the method works with whatever numbers you substitute.

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 $3.85 per US gallon, 35 US MPG, electricity at 25 cents per kWh and 3.5 miles per kWh — the petrol car costs about $0.11 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 ev vs petrol which is better for me

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. That is the point this page works through for ev vs petrol which is better for me.

Input Value used Status
Petrol price $3.85 per US gallon Example price
Petrol efficiency 35 US MPG Assumption
Electricity price 25 cents per kWh Example price
EV efficiency 3.5 miles per kWh Assumption
Annual mileage 10,000 miles Example

ev vs petrol which is better for me: 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 ev vs petrol which is better for me.

ev vs petrol which is better for me: Worked example: the same distance, two energy bills

Take a driver covering 10,000 miles a year. The petrol car does 35 MPG and petrol costs $3.85 per gallon as an example price, so its cost per mile is $3.85 ÷ 35 = $0.11, and 10,000 miles cost $1,100.00 a year. The EV does 3.5 miles per kWh and electricity costs 25 cents per kWh as an example price, so its cost per mile is $0.25 ÷ 3.5 = $0.07, and 10,000 miles cost $714.29 a year. The difference on fuel and charging alone is $385.71 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 which is better for me

The table uses the worked-example assumptions above — petrol at $3.85 per gallon (example), 35 MPG, electricity at 25 cents per kWh (example), 3.5 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 $660.00 $428.57 $231.43
8,000 $880.00 $571.43 $308.57
10,000 $1,100.00 $714.29 $385.71
12,000 $1,320.00 $857.14 $462.86
15,000 $1,650.00 $1,071.43 $578.57
20,000 $2,200.00 $1,428.57 $771.43

Cost per mile and per 100 miles for ev vs petrol which is better for me

At the example assumptions, the petrol car costs $0.11 per mile ($11.00 per 100 miles) and the EV costs $0.07 per mile ($7.14 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.

Break-even: how many miles before the EV pays back the price gap for ev vs petrol which is better for me

A break-even figure needs one more assumption: the price difference between the two cars. Suppose, as an example only, the EV costs $10,000.00 more than the comparable petrol car. The fuel and charging saving under this page's assumptions is $0.04 per mile, so the break-even distance is $10,000.00 ÷ $0.04 = 259,259 miles. At 10,000 miles a year that is about 25.9 years of driving. That figure counts fuel and charging only. It excludes insurance, depreciation, servicing differences, tyre wear, tax and any grants or incentives — name them, do not hide them — and each one moves the real break-even point. Depreciation alone can outweigh years of fuel savings, and insurance can differ enough to matter. A break-even number that hides those costs is not a like-for-like comparison, so use this page's figure as a starting point and add the excluded items with stated assumptions before deciding anything.

What the comparison leaves out — and why it matters for ev vs petrol which is better for me

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. That is the point this page works through for ev vs petrol which is better for me.

ev vs petrol which is better for me: Common mistakes

  • 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. That is the point this page works through for ev vs petrol which is better for me.
  • Taking ev vs petrol which is better for me as 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.
  • On this page, ev vs petrol which is better for me is the case in point: 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.
  • For ev vs petrol which is better for me, 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.

ev vs petrol which is better for me: Related calculations

On this page, ev vs petrol which is better for me is the case in point: These pages continue from here: the same method on a neighbouring question, or the calculator that runs the arithmetic for you.

Putting your figure to work for ev vs petrol which is better for me

Taking ev vs petrol which is better for me as the case in point: 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?

Taking ev vs petrol which is better for me as the case in point: 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.

Is an EV always cheaper to run than a petrol car?

Taking ev vs petrol which is better for me as the case in point: Not always. On fuel and charging alone, an EV is usually cheaper per mile when it charges mostly at home at an example electricity price, but the answer flips if it relies on expensive public rapid charging or if the petrol car is very efficient. Purchase price, depreciation, insurance and servicing are not in the fuel-cost maths, so a full comparison has to include them before calling either car cheaper overall.

Does an EV cost more to insure?

Taking ev vs petrol which is better for me 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.

Can I use the same method for a diesel car?

On this page, ev vs petrol which is better for me 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.

Should I use US or imperial gallons?

For ev vs petrol which is better for me, the point is this: Use the gallon your country uses, and say which one. A UK imperial gallon is about 4.55 litres and a US gallon is about 3.79 litres, so the same car shows a higher MPG number in imperial gallons. Mixing the two shifts the answer by about 20 percent with no warning.