The formula
Every calculator on this site is a different presentation of the same equation:
Petrol cost = (Distance ÷ Mileage) × Price per unit
The three inputs must agree on units — kilometres with km/L, miles with MPG, or kilometres with L/100 km. The calculator normalizes everything to a common base unit before applying the price; the user just picks the units they think in.
Unit conversions
- 1 mile = 1.609344 km (international agreement, 1959).
- 1 US gallon = 3.785411784 L. 1 UK gallon = 4.54609 L. The two are different — a US MPG figure does not carry over to UK fuel pricing.
- MPG → km/L: multiply US MPG by 0.4251. Equivalently, 25 US MPG ≈ 10.6 km/L.
- L/100 km → km/L: divide 100 by L/100 km. So 8 L/100km = 12.5 km/L.
Conversion references: the NIST Guide to the SI, Appendix B.8 publishes the international-mile and US MPG conversion factors. The European Union fuel-consumption information directive recognizes L/100 km, km/L, and compatible mile-and-gallon units for consumer fuel-consumption information.
Currency and price presets
The page starts with a neutral local-currency placeholder. If no saved preference exists, a first-use country lookup may suggest a currency and compatible units. Any displayed price is editable and is not a live quote, national average, or exchange-rate conversion.
For a transparent worked example, let P represent the current local price per litre entered by the user:
- 50 km at 10 km/L uses 5 litres.
- Total cost = 5 litres × P.
- Changing the currency label does not change or convert the number.
Confirm the current rate and volume unit at your local pump or through the official price source for your jurisdiction before relying on the result for a budget commitment.
Default mileage figures
The vehicle selector preloads illustrative mileage ranges for each segment. Replace these examples with a measured average for your own vehicle whenever possible:
- Bike (motorcycle): 35–65 km/L. Default 50 km/L (mid-range 125cc commuter).
- Scooter: 40–55 km/L. Default 50 km/L (typical city scooter).
- Car: 9–20 km/L. Default 14 km/L (small sedan / hatch).
- Truck / SUV: 7–13 km/L. Default 10 km/L (mid-size SUV / pickup).
Period projections
The general result panel uses simple 30-day and 365-day reference projections. The dedicated monthly and annual calculators instead multiply the daily result by the travel-day count entered by the user. Separate routes with different daily distances and add their results.
Carpool split
The carpool option divides the total trip cost by the number of riders, including the driver. So 4 carpoolers split an LCU 200 trip into LCU 50 each. The site does not automatically weight shares by distance. For unequal journeys, calculate the relevant route segments separately and agree on each person's contribution before using the carpool split calculator.
Where we're less precise
- We use a single mileage figure for the whole trip. Real-world fuel economy varies with stop-and-go traffic, hill grade, climate-control use, tyre pressure, vehicle age, load, and driving style.
- We assume the petrol price is constant across the trip. For out-of-region road trips, refill prices change.
- We don't separately model cold-start and warm-up fuel use on short trips; those effects are represented only if they are already reflected in the mileage figure you enter.
Disclaimer
Estimates only. The calculator is a budgeting and planning tool, not a fleet-management or tax-deduction system. Confirm fuel prices with your local pump and verify mileage against your own fill-up records before relying on the output for business expense reporting.