Fuel Efficiency

Gauging Efficiency: A Guide to Fuel Consumption Units

Fuel efficiency is a measure of how far a vehicle can travel on a specific amount of fuel. It's a critical factor for consumers choosing a car, for governments setting environmental standards, and for companies managing large vehicle fleets. Improving fuel efficiency directly reduces transportation costs for individuals and businesses and, on a larger scale, lowers greenhouse gas emissions and dependence on fossil fuels. However, the way we express this efficiency differs significantly around the world, which can make direct comparisons between vehicles from different markets challenging.

This converter is designed to clarify these differences by translating between the two main systems: 'distance per volume' and 'volume per distance'. In the United States and the UK, 'miles per gallon' (MPG) is the standard, where a higher number is better. In most other parts of the world, including Europe, Canada, and Australia, 'liters per 100 kilometers' (L/100km) is the standard, where a lower number is better. Our tool allows you to easily convert between these inverse relationships, as well as the more direct 'kilometers per liter' (km/L) used in other regions, making it simple to compare vehicle specifications from different countries and make informed decisions.

Relevant Formulas and Concepts

• Efficiency Calculation (Distance per Volume): Efficiency = Distance Traveled / Fuel Consumed. This is the basis for MPG and km/L.
• Consumption Calculation (Volume per Distance): Consumption = Fuel Consumed / Distance Traveled. This is the basis for L/100km.
• Inverse Relationship: The core formula to switch between the two main types of measurement is MPG ≈ 235.215 / (L/100km) and L/100km ≈ 235.215 / MPG.
• Work and Energy (Physics): The chemical energy (E) stored in fuel is converted by an engine into useful work (W) to move the vehicle against forces like air resistance (drag) and rolling friction. The thermal efficiency of this process (η = W/E) is the core of automotive engineering and a key determinant of fuel economy.

A Deep Dive into Common Fuel Efficiency Units

• Miles per Gallon (US) (MPG): This unit measures how many miles a vehicle can travel on one US gallon of fuel. It is the standard in the United States. A higher MPG value indicates better fuel efficiency. For example, a car that achieves 40 MPG is more efficient than one that achieves 25 MPG.
• Miles per Gallon (UK) (MPG): The same concept as US MPG, but it uses the larger Imperial Gallon. An Imperial Gallon is about 20% larger than a US Gallon, so a vehicle's MPG (UK) rating will be higher than its MPG (US) rating.
• Liters per 100 kilometers (L/100km): This unit measures how many liters of fuel a vehicle consumes to travel 100 kilometers. It is the standard in Canada, Europe, Australia, and many other parts of the world. In this case, a lower value indicates better fuel efficiency. A car that uses 5 L/100km is more efficient than one that uses 8 L/100km. This method is often argued to be more intuitive for calculating fuel costs for a trip.
• Kilometers per Liter (km/L): Similar in concept to MPG, this unit measures how many kilometers a vehicle can travel on one liter of fuel. It is used in some regions, particularly in Asia and South America. Like MPG, a higher km/L value is better.