Fuel Cost Calculator

How to use the Fuel Cost Calculator

Three inputs give you the complete fuel cost for any trip.

1. Choose metric or imperialClick the toggle at the top. Metric uses L/100km and price per litre. Imperial uses MPG and price per gallon.
2. Enter the trip distanceType the one-way or round-trip distance depending on the journey you are planning.
3. Enter your vehicle efficiencyUse the official fuel consumption figure from your vehicle manual or a measured average from past fill-ups. Furthermore, real-world efficiency is typically 10–20% higher than official figures.
4. Enter the fuel priceCheck the current pump price at your local station or use a price comparison app.
5. Read the resultsTotal cost, litres or gallons needed and cost per unit distance all appear at once. Furthermore, this makes it easy to compare the cost of different vehicles for the same trip.

Options and variants explained

Fuel efficiency units vary by country — the calculator handles both standards.

The formula explained

Cost per kilometre is derived by dividing total trip cost by distance. This is useful for comparing two vehicles: a car with lower fuel consumption per kilometre is cheaper to run even if its purchase price is higher, provided the distance driven justifies the saving.

Worked example: 500 km trip at 8.5 L/100km and $1.75/L

Fuel needed: 500 × 8.5 ÷ 100 = 42.5 litres. Cost: 42.5 × $1.75 = $74.38. Cost per kilometre: $74.38 ÷ 500 = $0.149/km. Furthermore, this forms the basis for mileage reimbursement calculations in a business context.

If the same trip were made in a more efficient vehicle at 6.0 L/100km, the fuel cost falls to $52.50 — a saving of $21.88. Over a year with 20,000 km of similar driving, the annual saving would be $875. Consequently, small efficiency improvements compound into significant costs over time.

Comparing vehicles on fuel cost

Enter the same trip distance for two vehicles at their respective efficiencies and prices. The tool gives a cost per kilometre for each. Moreover, multiplying the per-km difference by your annual kilometres gives the annual saving from choosing the more efficient vehicle.

What determines fuel consumption?

Fuel consumption depends on vehicle weight, engine size, aerodynamics, tyre rolling resistance and driving behaviour. City driving with frequent stops and starts typically consumes 20–40% more fuel than open-road driving. Furthermore, air conditioning adds roughly 10–20% to fuel use in stop-start traffic.

Speed has a quadratic effect on aerodynamic drag. At 130 km/h, aerodynamic drag is roughly double what it is at 90 km/h. Consequently, highway fuel consumption rises significantly above 110 km/h, and reducing motorway speed by 20 km/h can cut fuel use by 15–20%.

Vehicle load also matters. Each additional 50 kg of payload increases fuel consumption by approximately 2%. Therefore, removing heavy items from the boot and carrying only what is needed for a trip produces a measurable saving on longer journeys.

Why fuel cost calculations matter

Fuel is one of the largest variable costs of vehicle ownership. Accurately budgeting for it requires knowing your vehicle's real-world consumption, not just the official figure. Moreover, the gap between official and real-world consumption is largest in city driving, which is where most commuters accumulate their kilometres.

For businesses that reimburse employees for vehicle use, a per-kilometre rate must cover actual fuel costs at current prices. Furthermore, the rate should be recalculated whenever pump prices move significantly. This calculator provides the per-kilometre cost that feeds into accurate reimbursement policies.

For electric vehicles, the equivalent calculation uses electricity consumption in kWh per 100 km and the price per kWh. Moreover, the much lower energy cost of electricity versus petrol is the main financial argument for EV adoption, and comparing the two with real local prices makes the case concrete.

Common fuel cost calculation mistakes

Using the official fuel economy figure rather than a real-world average understates fuel costs. Official figures are measured under controlled laboratory conditions. Moreover, real-world consumption is typically 15–25% higher due to traffic, heating, air conditioning and driving style.

Forgetting to account for a round trip rather than one-way distance halves the projected cost. For a commute or recurring journey, multiply the one-way result by two or calculate directly with the round-trip distance. Furthermore, for annual budgeting, multiply the per-trip cost by the number of round trips per year.

Comparing vehicles on list price alone without considering fuel running costs misses a major ownership expense. A cheaper car with poor fuel economy can cost more over five years than a more expensive efficient model. Consequently, total cost of ownership — purchase price plus five years of fuel — is the correct comparison metric.

Tips for reducing fuel costs

Maintain correct tyre pressure at all times. Under-inflated tyres increase rolling resistance and fuel consumption by up to 3% per tyre. Furthermore, checking pressure monthly takes two minutes and the saving compounds over every kilometre driven.

Drive smoothly and anticipate stops. Harsh acceleration and late braking waste the kinetic energy that smooth driving preserves. Moreover, leaving adequate following distance allows coasting to slow naturally, which uses no fuel rather than burning more to maintain speed until the last moment.

Compare pump prices before filling up. Prices at the same station can vary by 10–15% across the week and by station. Additionally, loyalty programmes at supermarket-linked stations often add an effective per-litre discount worth tracking.

Frequently asked questions

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