Fuel Cost Calculator

Features

• Metric and imperial distances
• Four efficiency formats including both MPG variants
• Round-trip toggle
• Cost per passenger for shared journeys
• Shows the working so you can check it

How to use it

1. Enter the distance and pick its unit.
2. Enter your vehicle's efficiency in whichever format you know.
3. Enter the current fuel price.
4. Read the total and per-passenger cost.

Efficiency figures and why yours will be worse

Two things routinely trip people up. First, UK and US gallons differ, a UK gallon is 4.546 litres and a US gallon 3.785. A car rated at 40 MPG in the UK would be rated around 33 MPG in the US for identical real-world consumption, so comparing figures across the two systems without converting is meaningless. Second, L/100km and MPG run in opposite directions: lower is better for L/100km, higher is better for MPG, and the relationship between them is reciprocal rather than linear.

Manufacturer efficiency figures are obtained under standardised laboratory conditions. Europe's WLTP cycle replaced the older and notoriously optimistic NEDC in 2018 and is closer to reality, but real-world consumption still typically runs 10% to 20% worse. Short journeys are much worse than that, because an engine running below operating temperature can consume 50% more fuel over the first few kilometres.

The variables under your control are larger than most people assume. Aerodynamic drag rises with the square of speed, so cruising at 110 km/h instead of 130 cuts consumption noticeably on a long trip. A roof box can add 10% to 25%. Under-inflated tyres, aggressive acceleration and running the air conditioning at low speeds all add measurably. For a genuinely accurate figure, divide the fuel you actually put in by the distance you actually covered over several tanks.