Enter your fuel economy and pump price, the EV's consumption and your tariff, and the calculator returns cost per 100 km for both, the yearly gap, and how long a price difference between the two vehicles would take to pay back.
Is an EV cheaper to run than a petrol car?
Usually, if you charge at home. A car doing 8 L/100 km at 1.70 a litre costs 13.60 per 100 km in fuel; an EV using 16 kWh/100 km on a 0.30 tariff costs 4.80, about a third. Charging only on public DC at 0.70 per kWh raises it to 11.20, close to the petrol figure.
Fuel is where electric wins, and it wins big
A petrol car doing 8 L/100 km at 1.70 per litre costs 13.60 per 100 km. An efficient EV using 16 kWh/100 km on a 0.30 tariff costs 4.80 — roughly a third. Scale that to 15,000 km a year and the gap is around 1,300 a year, before you touch maintenance.
The comparison narrows if you charge exclusively on expensive public DC. At 0.70 per kWh the same EV costs 11.20 per 100 km, within a couple of units of the petrol car. This is the real reason home or workplace charging matters so much to EV economics — it is not convenience, it is the entire business case.
Fuel economy conversions
The single most common error in these comparisons is mixing US and imperial gallons. An imperial gallon is 20% larger, so “30 mpg” means two noticeably different things depending on which side of the Atlantic wrote it.
| L/100km | US mpg | Imperial mpg | km/L |
|---|---|---|---|
| 4.0 | 58.8 | 70.6 | 25.0 |
| 5.0 | 47.0 | 56.5 | 20.0 |
| 6.0 | 39.2 | 47.1 | 16.7 |
| 7.0 | 33.6 | 40.4 | 14.3 |
| 8.0 | 29.4 | 35.3 | 12.5 |
| 10.0 | 23.5 | 28.2 | 10.0 |
| 12.0 | 19.6 | 23.5 | 8.3 |
And the scooter case, which is not close
If the trip you are replacing is a short urban one, a scooter is not competing with a car on cost — it is annihilating it. A 500 Wh scooter covers 25 km on about 15 cents of electricity. The same trip in a petrol car costs 3–4 in fuel alone, plus parking. For the purchase side of the sum, see how much an electric scooter costs.
Set the EV column to scooter numbers — about 20 Wh/km including charging losses, so 2 kWh/100 km — and the per-100 km cost lands near 0.60. That is the arbitrage micromobility runs on, and it is why so many two-car households quietly became one-car-and-a-scooter households.
What this calculator deliberately leaves out
It compares energy, not everything. Insurance, depreciation, tyres, registration and repairs vary far too much by market and model to model meaningfully, and adding invented averages would make the answer look more precise than it is.
Two real-world adjustments worth making yourself: EVs generally cost less in servicing — no oil changes, no timing belts, far less brake wear thanks to regeneration — but they get through tyres faster because of weight and torque. Those two partly cancel, which is why energy cost remains the dominant term.
How the calculator works
Whatever units you enter, fuel economy is converted to litres per 100 km and fuel price to price per litre, so both vehicles are costed per 100 km on the same basis. Annual cost scales that by your yearly distance, and break-even divides the EV’s extra purchase price by the annual saving.
The electric side multiplies consumption by your tariff directly, so enter consumption measured at the wall. Official EPA figures already are; a car’s own trip computer usually is not, so add about 10% to it for charging losses.
The formula
Imperial mpg → L/100km = 282.481 ÷ mpg
break-even years = extra purchase cost ÷ annual saving
Related calculators
The comparison lives or dies on your electricity price, so pin that down with the charging cost calculator first. For the environmental side of the same switch, the CO₂ savings calculator uses your own grid rather than a national average.
Questions riders actually ask
How do I convert mpg to L/100km?
For US mpg: L/100km = 235.215 ÷ mpg. For UK (imperial) mpg: L/100km = 282.481 ÷ mpg. So 30 US mpg is 7.84 L/100km, while 30 UK mpg is 9.42 L/100km — a 20% difference that catches people out constantly.
What is the electric equivalent of miles per gallon?
MPGe, which the EPA defines by treating 33.7 kWh as energy-equivalent to one gallon of petrol. An EV using 30 kWh per 100 miles scores about 112 MPGe. It is useful for comparing EVs to each other but tells you nothing about cost, since electricity and petrol are priced completely differently.
Do EVs really need less maintenance?
Materially less on the drivetrain: no oil, filters, spark plugs, exhaust or gearbox service, and brake pads that often last two to three times longer because regeneration does most of the slowing. Tyres, suspension, cabin filters, coolant and wipers are unchanged, and tyres typically wear faster.
How long until an EV pays back its higher purchase price?
Divide the price difference by the annual energy saving. A 6,000 premium against a 1,300 yearly saving pays back in about 4.6 years — sooner with high mileage or expensive fuel, later if you charge publicly or drive very little. The break-even figure here does exactly that arithmetic.
Should I include the cost of installing a home charger?
Yes, as a one-off added to the price difference. A typical wallbox install is 800–1,500 depending on your electrics and any grant available. It usually adds about a year at most to break-even and more than halves your charging cost against public rates.
Sources
Primary and reference sources for the physics, standards and figures used on this page.
- The fuel economy label for electric vehicles (MPGe)FuelEconomy.gov
- Global EV Outlook 2025International Energy Agency