Fuel Economy Converter

Common Fuel Economy Conversions

Fuel Economy Standards Around the World

Fuel economy is measured differently depending on where you live. In the United States, fuel efficiency is expressed in miles per gallon (mpg), where a higher number means better efficiency. In most of Europe, South America, and much of Asia, the standard metric is liters per 100 kilometers (L/100km), an inverse measure where a lower number indicates better economy. Japan and several other countries use kilometers per liter (km/L), which, like mpg, is a direct measure where higher is better.

The key challenge in converting between these systems is that L/100km is an inverse metric. Unlike converting between miles and kilometers, which involves a simple multiplication factor, converting mpg or km/L to L/100km requires division. For example, doubling your mpg rating does not halve your L/100km value in a linear fashion. This is why our converter uses specialized formulas for each conversion pair rather than a single multiplication factor.

EPA Testing and WLTP vs. NEDC

In the United States, the Environmental Protection Agency (EPA) is responsible for testing and certifying the fuel economy ratings of all new vehicles sold. The EPA uses a series of standardized drive cycles that simulate city driving, highway driving, high-speed aggressive driving, air-conditioned driving, and cold-temperature operation. The final window-sticker values are adjusted downward from laboratory results to better reflect real-world conditions, typically reducing city ratings by about 10% and highway ratings by about 22%.

In Europe, the Worldwide Harmonized Light Vehicles Test Procedure (WLTP) replaced the older New European Driving Cycle (NEDC) in 2017. The NEDC was widely criticized for producing fuel economy figures that were significantly more optimistic than real-world driving. The WLTP uses more dynamic driving profiles, higher speeds, and longer test durations, resulting in figures that are typically 10-20% higher in fuel consumption compared to NEDC values. When comparing fuel economy ratings between US and European vehicles, it is important to account for these different testing methodologies.

Tips for Improving Fuel Economy

Regardless of the unit you use to measure it, improving your vehicle's fuel economy saves money and reduces emissions. Maintaining proper tire pressure can improve fuel economy by up to 3%, as under-inflated tires increase rolling resistance. Removing excess weight from your vehicle also helps, as every additional 100 pounds (45 kg) can reduce fuel economy by about 1%. Smooth, consistent driving with gentle acceleration and braking is more efficient than aggressive driving, which can lower highway fuel economy by up to 33%.

Regular maintenance, including timely oil changes, air filter replacements, and spark plug checks, keeps your engine running at peak efficiency. Using cruise control on highways maintains a steady speed and avoids unnecessary fuel consumption. Additionally, reducing idling time, planning routes to avoid congestion, and combining errands into single trips all contribute to better fuel economy. At highway speeds, closing windows and using air conditioning can actually be more efficient than open-window driving, which increases aerodynamic drag significantly.

Electric Vehicles and MPGe

As electric vehicles (EVs) become more common, a new metric has emerged: miles per gallon equivalent (MPGe). The EPA defines MPGe based on the energy content of one gallon of gasoline, which is approximately 33.7 kilowatt-hours (kWh). An EV rated at 100 MPGe, for example, can travel 100 miles on 33.7 kWh of electricity. This metric allows consumers to compare the energy efficiency of electric and gasoline vehicles on a common scale.

Most modern EVs achieve MPGe ratings well above 100, with some compact models exceeding 130 MPGe. By comparison, the most fuel-efficient conventional gasoline vehicles typically top out around 55-60 mpg. However, MPGe does not account for the efficiency of electricity generation or the cost difference between electricity and gasoline. For a complete comparison, drivers should also consider the cost per mile driven, which depends on local electricity rates and gasoline prices. Despite these nuances, fuel economy conversion tools remain valuable for understanding and comparing vehicle efficiency across different measurement systems and powertrain types.