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Fuel Economy Conversion: A Brief History and Guide Historical Development Fuel economy measurements emerged with the 1970s oil crisis when the US government mandated efficiency standards through CAFE (Corporate Average Fuel Economy) regulations in 1975. The EPA introduced standardized MPG testing in 1978, establishing city/highway cycles that remained largely unchanged until 2008 when more realistic test procedures were adopted. Europe developed the L/100km standard in the 1980s as part of metric harmonization, choosing consumption-per-distance over distance-per-consumption for easier fuel cost calculations. Primary Measurement Systems MPG (Miles per Gallon) measures distance traveled per fuel unit, used in US (US gallon = 3.785L) and UK (imperial gallon = 4.546L). Converting between them: UK MPG = US MPG × 1.201. The measurement favors higher numbers for better efficiency, making improvements seem more dramatic at lower efficiency levels. L/100km (Liters per 100 Kilometers) measures fuel consumed per standard distance, used in metric countries. Lower numbers indicate better efficiency. The inverse relationship with MPG means efficient vehicles show small differences (5 vs 6 L/100km) while inefficient vehicles show large gaps (15 vs 20 L/100km). km/L (Kilometers per Liter) primarily used in Japan, India, and some Asian countries, directly parallels MPG logic. Converting: km/L = 2.352 × MPG (US) or km/L = 100 ÷ L/100km. Key Conversion Formulas US MPG to L/100km: L/100km = 235.214 ÷ MPG L/100km to US MPG: MPG = 235.214 ÷ L/100km UK MPG to L/100km: L/100km = 282.481 ÷ MPG US MPG to UK MPG: UK MPG = US MPG × 1.201 km/L to L/100km: L/100km = 100 ÷ km/L Alternative Measurements MPGe (Miles per Gallon Equivalent) introduced in 2010 for electric vehicles, converts electrical energy (33.7 kWh) to gasoline energy equivalent. A Tesla Model 3 achieving 120 MPGe uses the same energy as a gas car getting 120 MPG would consume. kWh/100km or kWh/100mi measures electric vehicle efficiency directly, with typical EVs consuming 15-20 kWh/100km. Converting to MPGe: MPGe = 3370 ÷ kWh/100mi. Miles per kWh shows electric efficiency similar to MPG logic, with efficient EVs achieving 4-5 mi/kWh. This translates to about 120-150 MPGe. Regional Testing Differences EPA (US) tests include aggressive acceleration, air conditioning use, and high speeds since 2008 reforms, producing lower but more realistic numbers. NEDC (Europe, until 2017) used gentle acceleration and excluded accessories, producing optimistic figures often 20-30% higher than real-world consumption. WLTP (Europe, 2017+) introduced more realistic testing, increasing reported consumption by 10-20% over NEDC. Japan's JC08 cycle focuses on urban driving, making their figures less comparable internationally. Practical Conversion Examples 30 MPG (US) = 7.84 L/100km = 36 MPG (UK) = 12.75 km/L 6 L/100km = 39.2 MPG (US) = 47.1 MPG (UK) = 16.67 km/L 100 MPGe = 33.7 kWh/100mi = 21 kWh/100km The inverse relationship between MPG and L/100km creates confusion: improving from 10 to 20 MPG saves more fuel than improving from 30 to 40 MPG, though the numerical gain appears equal. This mathematical quirk led many countries to adopt consumption-based metrics for clearer cost comparisons.