How to Convert Miles per Gallon (US) to Liters per 100 Kilometers
Converting Miles per Gallon (mpg) to Liters per 100 Kilometers (L/100km) translates between the American fuel economy standard and the European fuel consumption standard. These two systems measure the same thing but from opposite perspectives: mpg measures distance per fuel volume (higher is better), while L/100km measures fuel volume per distance (lower is better). This inverse relationship makes the conversion non-linear, meaning equal increments in mpg do not translate to equal changes in L/100km. The conversion is critical for Europeans purchasing American vehicles, Americans buying European cars, and international automotive journalists comparing vehicles across markets. The European L/100km standard is used throughout the European Union, Australia, and many other countries. Understanding this conversion is also important for environmental policy comparisons, as EU emissions regulations are closely tied to L/100km consumption figures. The mathematical relationship involves both the mile-to-kilometer and gallon-to-liter conversions, combined with the inversion from "per gallon" to "per 100 km," making this one of the more complex fuel economy unit conversions.
Conversion Formula
The conversion from mpg to L/100km uses an inverse formula because the two units measure reciprocal quantities. The constant 235.214583 is derived from: (100 km / 1.609344 km per mile) * (3.785411784 liters per gallon) = 235.214583. You divide this constant by the mpg value because higher mpg (better efficiency) corresponds to lower L/100km (less fuel consumed).
L/100km = 235.214583 / mpg
30 miles per gallon (us) = 7.84 liters per 100 kilometers
Step-by-Step Example
To convert 30 mpg to L/100km:
1. Start with 30 mpg
2. Use the inverse formula: L/100km = 235.214583 / mpg
3. L/100km = 235.214583 / 30 = 7.84 L/100km
A car achieving 30 mpg consumes approximately 7.84 liters of fuel per 100 kilometers. In Europe, this would be considered reasonable fuel consumption for a mid-size gasoline vehicle.
Understanding Miles per Gallon (US) and Liters per 100 Kilometers
What is a Miles per Gallon (US)?
Miles per gallon originated as a natural way to express fuel economy in countries using the Imperial measurement system. In the United States, mpg became critically important after the 1973 OPEC oil embargo triggered fuel shortages and price spikes. The Energy Policy and Conservation Act of 1975 established CAFE standards measured in mpg, and the EPA began requiring fuel economy window stickers on all new vehicles. This made mpg one of the most consumer-facing measurement units in America, directly influencing vehicle purchasing decisions for over five decades.
What is a Liters per 100 Kilometers?
Liters per 100 kilometers became the standard fuel consumption measure in Europe and many other countries following metrication. The European Union adopted L/100km as the standard for vehicle fuel consumption labeling under Directive 80/1268/EEC and its successors. The "per 100 km" scaling was chosen to produce convenient whole numbers for typical vehicle consumption. The NEDC (New European Driving Cycle) and its successor WLTP (Worldwide Harmonized Light Vehicles Test Procedure) both report consumption in L/100km, cementing its role in European automotive regulation.
Practical Applications
European consumers shopping for American vehicles need this conversion to understand fuel costs in their local measurement system. Car comparison websites displaying international vehicle data convert between mpg and L/100km for side-by-side comparisons. Rental car companies operating in both US and European markets provide consumption figures in both formats. Climate policy researchers use this conversion when comparing fuel efficiency standards between the US (CAFE in mpg) and the EU (CO2 emissions closely linked to L/100km). Automotive engineers developing global vehicle platforms need both figures for regulatory compliance documents.
Tips and Common Mistakes
The most important thing to remember is that this is an inverse conversion, not a simple multiplication. Doubling your mpg does not double the L/100km value; it halves it. This non-linear relationship means that improvements at the low mpg end (e.g., 10 to 20 mpg) save much more fuel than the same mpg improvement at the high end (e.g., 40 to 50 mpg). Another critical error is confusing US gallons with Imperial gallons, which gives a constant of 282.481 instead of 235.215. Ensure you are using the correct gallon type for your source data.
Frequently Asked Questions
Because mpg measures distance per volume while L/100km measures volume per distance. These are reciprocal (inverse) quantities. Converting between them requires division by the mpg value, not multiplication. This means the relationship is a hyperbola: small mpg improvements at the low end produce large L/100km reductions, while the same mpg improvement at the high end produces smaller L/100km reductions.