Fuel cost calculator
What petrol and electric actually cost to run, side by side — including the part most comparisons skip, which is how much of your charging happens at a public rapid charger.
I drivea year.
Petrol / diesel
Electric
Electric saves you
$680
a year · $3,400 over five years
- Petrol / diesel
- $1,400
- per year
- Electric
- $720
- per year
- Fuel per mile
- $0.12
- 1,514 L a year
- Electric per mile
- $0.06
- 3,429 kWh a year
›Public charging, purchase premium and currency
Fuel and charging only. Insurance, servicing, depreciation, road tax and charger installation all move the real answer and none are included.
The gallon problem
Fuel economy is the one place where an honest-looking number can be wrong by a fifth. The imperial gallon and the US gallon are different volumes, and both are written “mpg”.
US gallon 3.785411784 L imperial gallon 4.54609 L → 20.1% larger mpg (US) → L/100km 235.21 ÷ mpg mpg (imp) → L/100km 282.48 ÷ mpg 30 mpg (US) = 7.84 L/100 km 30 mpg (imp) = 9.42 L/100 km ← same number, different car
Everything above is normalised to litres per 100 km and a price per litre before any arithmetic runs, so mixing units in the inputs cannot corrupt the result.
Questions
›Is US mpg the same as UK mpg?
No, and the gap is large. An imperial gallon is 4.546 litres against the US gallon's 3.785, so the same car rates about 20% higher in UK mpg than US mpg. A car doing 30 mpg in the US does roughly 36 mpg imperial. This calculator asks which one you mean.
›How do I convert mpg to L/100 km?
Divide 235.21 by the US mpg figure, or 282.48 by the imperial figure. The two scales run in opposite directions: higher mpg is better, lower L/100 km is better.
›What electricity rate should I use?
Your home rate is on your energy bill in cost per kWh. Public rapid charging typically runs two to four times that, which is why the home-charging share matters so much — an EV charged mostly in public can cost more to run than a petrol car.
›What counts as good EV efficiency?
Roughly 3 to 4 miles per kWh, or 15 to 20 kWh per 100 km, covers most current electric cars. Large SUVs and pickups sit below that; small hatchbacks can beat it. Cold weather can cost 20–30%.
›Does this include the cost of buying the car?
Only if you enter a purchase premium, which the calculator uses to work out payback time. Insurance, servicing, depreciation, road tax and home charger installation are not included, and any of them can change the real answer.
Converting a single figure? mpg to L/100 km tables.