EV vs Gas Calculator: What the Maths Really Says

If you want a straight answer on ev vs gas calculator, start with the maths, not a guess. This page works through the formula step by step, runs a worked example with the assumptions stated in full, and gives you a table you can read your own numbers off. Everything here uses the same definitions throughout, so the figures in the table match the figures in the example.

The short version is that ev vs gas calculator comes down to two measurements you can take yourself: how far you drove, and how much fuel you used. Get those two right and the rest is arithmetic. Get either one wrong — a half-full tank, a trip meter that was never reset, a gallon confused with a litre — and the answer is meaningless, however carefully you divide.

How the EV versus petrol cost comparison works — ev vs gas calculator

To compare an EV with a petrol car fairly, hold the mileage constant and price the energy each one actually uses. A petrol car burns gallons, so its cost per mile is the price per gallon divided by its MPG. An EV uses kilowatt-hours, so its cost per mile is the price per kWh divided by its miles per kWh. This page works the example with stated assumptions: petrol at $4.05 per gallon (example price), 40 MPG for the petrol car, electricity at $0.16 per kWh (example price), and 3.2 miles per kWh for the EV. Change any one of those and the answer moves — cheap home charging helps the EV, expensive public rapid charging hurts it, and a very efficient petrol car narrows the gap. The sections below show the result at several mileages so you can see how the saving scales, and they name what is excluded: purchase price, depreciation, insurance, servicing and tax are not in this fuel-cost maths.

Worked example: the same miles, two fuel bills — ev vs gas calculator

Take a driver covering 12,000 miles a year. The petrol car in this example does 40 MPG and petrol costs $4.05 per gallon as an example price, so its cost per mile is $4.05 ÷ 40 = $0.10 per mile, and 12,000 miles cost 12,000 × $0.10 = $1,215.00 a year. The EV does 3.2 miles per kWh and electricity costs $0.16 per kWh as an example price, so its cost per mile is $0.16 ÷ 3.2 = $0.05 per mile, and 12,000 miles cost $600.00 a year. The difference on fuel and charging alone is $615.00 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 — ev vs gas calculator

The table uses the worked-example assumptions above — petrol at $4.05 per gallon (example), 40 MPG, electricity at $0.16 per kWh (example), 3.2 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 $607.50 $300.00 $307.50
10,000 $1,012.50 $500.00 $512.50
12,000 $1,215.00 $600.00 $615.00
15,000 $1,518.75 $750.00 $768.75
20,000 $2,025.00 $1,000.00 $1,025.00

What the comparison leaves out — and why it matters — ev vs gas calculator

The honest way to read any EV versus petrol figure is to ask what went into it. For ev vs gas calculator, the same reasoning applies — substitute your own prices and efficiencies and the steps on this page still hold. On this page the inputs are stated: example fuel and electricity prices, an example MPG and an example miles-per-kWh figure, and the same annual mileage for both cars. What is not in the maths is just as important — the purchase-price gap, depreciation, insurance, servicing and tax. Those are real costs, and leaving them out does not make them disappear; it just narrows the question to fuel and charging alone. A break-even year calculated on fuel alone is therefore a partial answer. State it as one, and if you want the full answer, add the other costs with their own stated assumptions rather than guessing them.

Common mistakes — ev vs gas calculator

The most common mistake is mixing gallons: US and imperial gallons differ by about 20 percent, so a figure converted with the wrong gallon is wrong by the same margin. That is the point to carry into ev vs gas calculator: the answer follows from the assumptions, so write yours down before you trust the result. Next is trusting a single tank — one short fill or one unusual journey can tilt it badly — instead of averaging several. Third is reading the trip meter without resetting it at the fill, which mixes miles from before the fill into the calculation. Fourth is using the tank's capacity instead of the gallons actually pumped; the capacity is not the amount you used. And fifth is comparing a dashboard figure with a brim-to-brim figure as if they were the same measurement: the dashboard estimates from the engine's data, the brim-to-brim method measures what actually went in, and they disagree by a few percent in either direction.

Related calculations — ev vs gas calculator

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. Read the figures on this page about ev vs gas calculator as a worked illustration, not as prices or efficiencies you should quote elsewhere.

Putting your ev vs gas calculator figure to work

Putting the figure to work is where the method pays off. Read the figures on this page about ev vs gas calculator as a worked illustration, not as prices or efficiencies you should quote elsewhere. Once you know your own MPG, measured brim-to-brim over several tanks, you can price any journey before you set off: multiply the miles by the fuel price divided by your MPG, and the answer is the fuel cost of that trip at that example price. You can also compare cars honestly, because you are comparing measured figures rather than brochure claims. Keep a simple log — date, miles, gallons, price — and review it monthly. Patterns show up quickly: a winter dip, a motorway improvement, a slow decline that points to tyre pressures or a change in routes. The log turns a vague feeling about fuel use into a number you can act on, and that is the whole point of measuring in the first place.

Frequently asked questions

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

Not always. That is the point to carry into ev vs gas calculator: the answer follows from the assumptions, so write yours down before you trust the result. 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.

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

Use the same mileage for both cars. Read the figures on this page about ev vs gas calculator as a worked illustration, not as prices or efficiencies you should quote elsewhere. 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.

What is excluded from the EV versus petrol comparison?

Purchase price, depreciation, insurance, servicing, tyre wear and tax. Read the figures on this page about ev vs gas calculator as a worked illustration, not as prices or efficiencies you should quote elsewhere. This page compares fuel and charging costs only, and says so, because a break-even figure that hides those costs is not a like-for-like comparison. Add them with stated assumptions if you want a total-cost answer.

Does charging at home really make that much difference?

Yes, usually more than any other single factor. That is the point to carry into ev vs gas calculator: the answer follows from the assumptions, so write yours down before you trust the result. Home charging is typically far cheaper per kWh than public rapid charging, so a driver who charges at home overnight will see a much bigger saving than one who relies on rapid chargers. Work out your own mix of home and public charging and price each part separately for an honest figure.

How sensitive is the saving to the electricity price?

Very sensitive. For ev vs gas calculator, the same reasoning applies — substitute your own prices and efficiencies and the steps on this page still hold. 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.