Fuel Cost Comparison Calculator
Compare two cars on what they cost per 100 km, whatever they run on, and see how far you drive before a higher purchase price pays for itself.
Results
The dashed line marks the value you entered.
What this tool does
Petrol against diesel, petrol against electric, the car you have against the car you are looking at: the comparison is always the same shape. Take what each one uses per 100 kilometres, multiply by the price of what it uses, and you have two numbers that can be put side by side. Add the difference in purchase price and the page tells you how many kilometres — and how many years at your mileage — it takes before the cheaper one to run has paid back the more expensive one to buy.
Formula
cost/100 km = consumption/100 km × unit price ; km to break even = price difference ÷ savings/km
Variables
| Symbol | Meaning | Unit |
|---|---|---|
ca | First car, per 100 km | — |
pa | Price of its fuel or electricity | — |
cb | Second car, per 100 km | — |
pb | Price of its fuel or electricity | — |
km | Kilometres a year | km |
ex | How much more the second costs to buy | — |
A | First car, per 100 km | — |
B | Second car, per 100 km | — |
S | Saved in a year | — |
K | Kilometres to pay back the difference | km |
Y | Years to pay it back | a |
W | Cheaper to run | — |
Worked example
- First car, per 100 km6.5
- Price of its fuel or electricity1.75
- Second car, per 100 km17
- Price of its fuel or electricity0.22
- Kilometres a year15,000 km
- How much more the second costs to buy8000
- First car, per 100 km11.38
- Second car, per 100 km3.74
- Saved in a year1145.25
- Kilometres to pay back the difference104,781 km
- Years to pay it back7.0 a
- Cheaper to runThe second one
Limitations
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.
- This is an informational calculator, not personalised financial advice. Rates, fees, taxes and contract conditions vary between institutions and countries.
Frequently asked questions
How do I compare a petrol car with an electric one?
Put litres per 100 km and the price per litre on one side, and kWh per 100 km and the price per kWh on the other. The two units never meet, but the two costs per 100 km do, and that is the only comparison that means anything. Note that the price per kWh is where most of these comparisons go wrong: charging at home overnight and charging at a motorway rapid charger can differ by a factor of four.
Is fuel the whole story?
No. This page compares what goes in the tank or the battery and the difference in purchase price, which is the part people usually mean. Insurance, servicing, tyres, road tax and the way each car loses value are not here and can easily be larger than the fuel gap. The break-even figure is a floor, not a verdict.