⛽ Fuel Cost Calculator

What the calculation covers

Fuel cost for a journey is straightforward: divide distance by efficiency to get the fuel needed, then multiply by price per unit.

Cost = (distance ÷ efficiency) × price per unit

Watch the units. Miles per gallon, litres per 100 km, and kilometres per litre are all in common use, and they are not interchangeable — MPG and km/L go up as efficiency improves, while L/100km goes down. US and imperial gallons also differ by about 20 percent, so a US MPG figure and a UK MPG figure describe different things.

Why real economy falls short of the rating

Manufacturer figures come from standardised test cycles. Real-world consumption is usually 10 to 20 percent worse, and the gap widens in certain conditions.

Speed. Aerodynamic drag rises with the square of velocity, so power demand rises with the cube. Most cars are most efficient somewhere between 70 and 90 km/h; sustained motorway speeds above 110 km/h cost noticeably more fuel per kilometre.

Driving style. Hard acceleration and late braking convert fuel into heat in the brakes. Smooth anticipation is the single largest lever most drivers have, worth 10 to 20 percent.

Cold and short trips. An engine below operating temperature runs rich and burns significantly more fuel. Journeys under a few kilometres can consume twice the steady-state rate.

Load and pressure. Roof boxes wreck aerodynamics. Underinflated tyres raise rolling resistance — checking pressures monthly is one of the cheapest efficiency gains available.

Comparing routes and vehicles honestly

A longer motorway route often costs less fuel than a shorter urban one, because stop-start driving is far less efficient. When comparing, use realistic consumption for each road type rather than a single average.

For total cost of a journey, fuel is only part of it. Tolls, parking, and the per-kilometre share of maintenance and depreciation all belong in a fair comparison against rail or air. Many published cost-per-mile figures include those; fuel alone typically accounts for less than half of the true cost of driving.

Common questions

Does air conditioning use much fuel?

At low speeds it can add several percent. At motorway speeds, open windows create enough drag that air conditioning is often the more efficient choice.

Is premium fuel worth it?

Only if the engine is designed for higher octane. In a car specified for regular fuel, premium delivers no measurable benefit.

How do I compare with an electric vehicle?

Convert both to cost per 100 km. Electricity price varies enormously between home overnight charging and public rapid charging, so use the rate you would actually pay.