How this works
Fuel cost depends on three numbers: how far you drive, how efficiently the vehicle uses fuel, and how much each litre/gallon costs. The calculation is straightforward — fuel_used = distance / efficiency, then total_cost = fuel_used × price — but the choice of efficiency unit can confuse drivers crossing markets.
Three common units: (1) MPG (miles per gallon, US): popular in the US and historically the UK; higher numbers are better. (2) L/100 km (litres per 100 kilometres): Europe and most of the world; lower numbers are better, since it expresses consumption rather than range. (3) km/L (kilometres per litre): common in Japan, India, and parts of Asia; higher is better. This calculator accepts all three and converts internally.
A few honest caveats. Manufacturer-published efficiency (EPA, WLTP) is best-case; real-world consumption typically runs 10–20% worse, more if you drive uphill, in cold weather, with heavy load (roof box, towing), or with aggressive acceleration and braking. To budget realistically, use your actual measured efficiency over a few full tanks (use the Gas Mileage calculator), not the spec sheet. Plug-in hybrids and EVs use a different metric (miles per kWh or Wh per mile) — this calculator is for combustion engines.
The formula
distance is the trip length in your chosen unit. efficiency is the vehicle's consumption. price_per_unit is the cost of one unit of fuel (litre or gallon) at current pump prices. Use a single, consistent volume unit (litre OR gallon) for both efficiency and price.
Example calculation
- 500 km trip, car consumes 7.5 L/100km, fuel is €1.80/L.
- Fuel = 500 × 7.5 / 100 = 37.5 L. Cost = 37.5 × 1.80 = €67.50.
Frequently asked questions
How do I convert between MPG and L/100km?
L/100km = 235.215 / MPG (US). For UK gallons it's 282.481 / MPG. They are reciprocal — one measures consumption, the other range — so 30 MPG (US) ≈ 7.84 L/100km, and 8 L/100km ≈ 29.4 MPG (US). The factor 235.215 comes from converting one US gallon (3.78541 L) over 100 miles (160.934 km).
Why is real fuel consumption higher than the spec?
Lab tests (EPA, WLTP) use controlled rolling-road cycles with smooth acceleration, no AC, ideal temperature, and no wind. Real driving has hills, traffic, cold starts, AC/heater load, headwinds, roof bars, full passengers, and aggressive throttle. Plan for 10–20% worse than the spec, more in winter or with a roof box.
How do I find my real-world MPG?
Brim-fill the tank, reset the trip meter, drive normally for at least 2–3 full tanks, then brim-fill again and divide miles (or km) driven by gallons (or litres) added. The on-board computer is convenient but typically optimistic by 5–10%. The Gas Mileage calculator on calcso lets you compute it for any pair of refuels.