Fuel Efficiency Converter

Fuel Efficiency Converter – Convert MPG, L/100km, km/L and More

The Fuel Efficiency Converter lets you instantly convert vehicle fuel economy figures between all major units used worldwide. Whether you are comparing a US car rated at 35 mpg (US) with a European model rated at 6.5 L/100km, evaluating a Japanese import spec in km/L, or converting fleet data for analysis, this tool gives you accurate results across seven units with adjustable decimal precision.

All conversions are performed instantly in your browser using internationally standardized constants — no server calls, no account required.

Supported Fuel Efficiency Units

• mpg (US) — Miles per Gallon (US): The US gallon equals 3.785 liters. This is the standard unit for fuel economy ratings in the United States, printed on every new vehicle sticker and published by the EPA.
• mpg (UK) — Miles per Gallon (Imperial): The UK (Imperial) gallon equals 4.546 liters — about 20% larger than the US gallon. The same vehicle always shows a higher figure in mpg (UK) than in mpg (US), so it is important to check which standard is being used before comparing models.
• L/100km — Liters per 100 Kilometers: The most widely adopted unit globally, used across Europe, Australia, Canada, China, and most of Asia. Lower values mean better efficiency. This is the internal pivot unit used by the converter.
• km/L — Kilometers per Liter: Standard in Japan, India, and South Korea. Higher values mean better efficiency — the direct inverse relationship to L/100km.
• mi/L — Miles per Liter: Rarely encountered in everyday use but appears in academic papers and some engineering contexts. It is the imperial distance equivalent of km/L.
• L/km — Liters per Kilometer: Used in engineering for large vehicles and industrial equipment. Multiply by 100 to get L/100km.
• gal/100mi (US) — US Gallons per 100 Miles: An inverse form of mpg used in US fuel economy policy analysis and fleet management. Lower is more efficient, analogous to L/100km in structure.

How Fuel Efficiency Conversion Works

Every conversion uses L/100km as the internal pivot unit. The input value is first converted to L/100km using the source unit's formula, then that intermediate value is converted to the target unit. This two-step normalization approach ensures consistent accuracy across all unit combinations without accumulating rounding errors.

Key conversion formulas from any unit to L/100km:

• mpg (US) → L/100km: divide 235.2146 by the mpg value
• mpg (UK) → L/100km: divide 282.4809 by the mpg value
• km/L → L/100km: divide 100 by the km/L value
• mi/L → L/100km: divide 100 by (mi/L × 1.60934)
• L/km → L/100km: multiply L/km by 100
• gal/100mi (US) → L/100km: multiply by 3.785411784 ÷ 1.609344

Fuel Cost Estimator

Enable the Fuel Cost Estimator to calculate the total fuel consumed and estimated cost for a journey. Enter the trip distance in kilometers and the local fuel price per liter. The tool converts your vehicle's efficiency to L/100km, then applies the formula:

Fuel Used (L) = (L/100km ÷ 100) × Distance (km)
Total Cost = Fuel Used (L) × Price per Liter

For example, a car rated at 8 L/100km driving 500 km at a fuel price of 1.60 per liter consumes 40 liters and costs 64.00 in local currency.

CO2 Emissions Estimator

The CO2 Emissions Estimator calculates approximate carbon dioxide output for a given distance. Select your fuel type — gasoline, diesel, or LPG — and enter the annual or trip distance in kilometers. The tool uses standard combustion emission factors: gasoline 2.31 kg CO2/L, diesel 2.68 kg CO2/L, and LPG 1.61 kg CO2/L. These factors are widely used by environmental agencies for approximate vehicle emissions calculations.

For example, a car rated at 6.5 L/100km driven 12,000 km per year on gasoline consumes 780 liters of fuel and emits approximately 1,802 kg of CO2. Actual emissions depend on driving style, engine condition, and fuel blend.

US Gallon vs UK Gallon — A Common Source of Confusion

The most frequent mistake when comparing fuel economy across regions is confusing US and UK gallons. Because the UK Imperial gallon is 20% larger than the US gallon, a vehicle rated at 40 mpg (UK) is actually less fuel-efficient than one rated at 40 mpg (US). Specifically, 40 mpg (UK) ≈ 33.3 mpg (US) ≈ 7.07 L/100km, while 40 mpg (US) ≈ 48.1 mpg (UK) ≈ 5.88 L/100km. Always verify which standard applies before drawing conclusions.

Practical Applications

• Importing or renting vehicles abroad: Convert the manufacturer's fuel economy rating to your familiar unit before calculating running costs.
• Fleet management: Standardize fuel consumption data from vehicles sourced in different countries onto a single unit for analysis.
• Environmental reporting: Estimate CO2 output for a vehicle fleet or individual car based on annual mileage and fuel type.
• Trip cost planning: Combine efficiency, fuel price, and distance to budget accurately for road trips, especially across regions with different fuel costs.
• Academic and engineering use: Convert between less common units like mi/L, L/km, and gal/100mi for research papers or industrial specifications.

Efficiency Rating Scale

The tool shows a qualitative efficiency rating based on the equivalent L/100km value, reflecting broadly accepted benchmarks for passenger vehicles:

• Excellent — below 5 L/100km (above ~47 mpg US): hybrid, EV-equivalent efficiency
• Good — 5–7 L/100km (~34–47 mpg US): efficient modern petrol or diesel
• Average — 7–10 L/100km (~24–34 mpg US): typical family car
• Below Average — 10–14 L/100km (~17–24 mpg US): larger SUVs and trucks
• Poor — above 14 L/100km (below ~17 mpg US): heavy vehicles or performance cars