Fuel Economy Converter

What Is a Fuel Economy Converter?

A fuel economy converter translates a vehicle's fuel efficiency figure from one unit to another. Fuel economy, which measures how far a vehicle can travel on a given amount of fuel, is expressed differently across the world. The United States uses miles per US gallon (MPG). The United Kingdom uses miles per Imperial gallon (also called MPG, but with a different gallon). Continental Europe, Canada, Australia, China, and most of the rest of the world use litres per 100 kilometres (L/100km). Japan, India, and South Korea use kilometres per litre (km/L).

The result is a global landscape where the same car can appear to have four completely different fuel economy figures depending on which country's labeling standard you are reading. A 2025 Toyota Prius might be listed as 57 MPG in the United States, 68.4 MPG in the United Kingdom, 4.1 L/100km in Germany, and 13.9 km/L in Japan. All four numbers describe exactly the same fuel consumption. The only difference is the unit.

According to FuelEconomy.gov, the official US Department of Energy and EPA source for fuel economy information, the average fuel economy of new US passenger cars and light trucks reached 25.4 MPG combined in model year 2020. Converting that to L/100km (235.215 divided by 25.4) gives 9.26 L/100km. To a European driver, 9.26 L/100km reads as average to poor; to an American driver, 25.4 MPG reads as respectable. The underlying fuel consumption is identical.

This converter handles four main fuel economy units: MPG (US), MPG (UK/Imperial), L/100km, and km/L. It is designed for cross-border car buyers, expats adjusting to new measurement systems, fleet managers consolidating international vehicle data, and anyone comparing fuel efficiency specs that were published in different countries. According to Natural Resources Canada, Canadian vehicle fuel consumption labels display both L/100km and MPG (Imperial), reflecting the country's position between the US and European measurement traditions.

How to Use the Fuel Economy Converter

1. Enter your value. Type the fuel economy figure you want to convert. For example, 35 MPG, 8.5 L/100km, or 12.5 km/L. Decimal values are fully supported.
2. Select the source unit. Choose whether your value is in MPG (US), MPG (UK/Imperial), L/100km, or km/L. This step matters more than it might seem: choosing MPG (US) instead of MPG (UK) for the same number produces a result that is 20% different.
3. Read all equivalents at once. The converter displays your value in all four units simultaneously. You can verify the result against the reference benchmarks in the table below.
4. Remember direction. MPG and km/L follow the higher-is-better rule. L/100km follows the lower-is-better rule. Do not compare fuel efficiency by comparing the raw number across systems: 8 L/100km is more efficient than 25 MPG(US) because 8 L/100km equals 29.4 MPG(US), which is better than 25 MPG(US).
5. For UK vs. US MPG confusion: if the source does not specify which gallon standard the MPG figure uses, check the country of publication. UK car reviews, UK dealer listings, and WLTP figures always use Imperial gallons. US EPA window stickers, US dealer listings, and US car reviews always use US gallons. When in doubt, convert both to L/100km for a neutral comparison.

MPG (US) vs. MPG (UK) vs. L/100km: Key Fuel Economy Units Compared

The most important fact in fuel economy conversion: UK MPG is always approximately 20% higher than US MPG for the same vehicle. One Imperial gallon equals 4.546 litres; one US gallon equals 3.785 litres. The Imperial gallon is 20.09% larger. A car that achieves 50 MPG by UK measurement (WLTP or old NEDC cycle) achieves only 41.6 MPG by US measurement (EPA cycle). These figures cannot be compared directly without specifying the gallon standard.

The inverse relationship: MPG and L/100km do not convert by simple multiplication. They are reciprocal units. The formula is L/100km = 235.215 divided by MPG(US). This means the MPG scale is non-linear: the fuel saving from improving 10 MPG to 20 MPG (117.6 L saved per 1,000 km) is far larger than the saving from improving 40 MPG to 50 MPG (29.4 L saved per 1,000 km). L/100km makes this fuel saving immediately visible as a linear reduction; MPG obscures it.

Reference benchmarks (2025 US EPA figures): Toyota Prius 57 MPG (4.1 L/100km); Toyota RAV4 Hybrid 41 MPG (5.7 L/100km); Honda Civic 36 MPG (6.5 L/100km); Ford F-150 V8 4WD 18 MPG (13.1 L/100km); US fleet average 25.4 MPG (9.3 L/100km).

When to Use a Fuel Economy Converter

The American Moving to Canada

Jake is an American engineer relocating to Toronto. He wants to buy a Honda CR-V. The Canadian dealer's listing shows 8.1 L/100km city, 6.3 L/100km highway. Jake has spent his whole driving life thinking in MPG and has no intuition for what those numbers mean. Converting: 8.1 L/100km equals 235.215 divided by 8.1 = 29.0 MPG(US) city; 6.3 L/100km equals 235.215 divided by 6.3 = 37.3 MPG(US) highway. Those are familiar, comfortable numbers. His current car gets 28 MPG city, so the CR-V is a slight improvement. But Jake also notices that his Canadian colleague tells him the CR-V gets "35 MPG city" on the Canadian spec sheet. That figure uses Imperial gallons: 235.215 divided by 8.1 km multiplied by the Imperial-to-US ratio = actually 34.8 MPG(UK), not the same as the 29.0 MPG(US) he calculated. Without the converter, Jake nearly believes the Canadian CR-V is significantly more efficient than his American one, when in fact they are identical vehicles with the same fuel consumption.

The British Expat Buying a Car in Australia

Sarah moved from London to Sydney. She is comparing two used cars: a Toyota Camry listed at 7.5 L/100km and a Mazda6 listed at 7.8 L/100km. She keeps instinctively thinking "that sounds like about 37 MPG" but cannot be sure whether her mental conversion is using Imperial or US gallons. Converting: 7.5 L/100km equals 282.481 divided by 7.5 = 37.7 MPG(UK) or 235.215 divided by 7.5 = 31.4 MPG(US). In the UK, she was accustomed to thinking of 40-plus MPG as good. In Australian L/100km terms, anything below 8.0 is respectable for a mid-size sedan. The converter confirms both cars are in the expected range. The key insight the converter gives Sarah is that her mental benchmark (40 MPG UK = 7.1 L/100km) translates correctly and she can calibrate her expectations for the Australian market without rebuilding her fuel economy intuition from scratch.

The International Fleet Manager

David manages a fleet of 200 vehicles across the UK, Germany, the United States, and India. His UK vans report fuel economy to company policy in MPG(UK). His German vans report in L/100km. His US trucks report in MPG(US). His Indian motorcycles report in km/L. When compiling quarterly fleet efficiency reports for the board, he must convert all 200 figures into a single standard (L/100km) for meaningful comparison. A single data entry error, using the US gallon formula for a UK vehicle, produces a result that is 20% wrong and distorts the UK fleet's performance against the German fleet. For David, the fuel economy converter is not a curiosity; it is a financial controls tool. An incorrect conversion in a 40-vehicle UK fleet produces a distortion equivalent to approximately 8 vehicles' worth of phantom fuel savings in the quarterly report.

The EV Shopper Comparing MPGe to MPG

Mia is choosing between a Toyota Prius and a Tesla Model 3 in the United States. The Prius window sticker shows 57 MPG combined. The Tesla window sticker shows 134 MPGe. She wants to know how to compare these, and what the figures mean in L/100km for her upcoming two-year move to Germany. MPGe (miles per gallon of gasoline-equivalent) is the EPA standard for electric vehicles, based on the energy content of one US gallon of gasoline being equal to 33.7 kWh. At 134 MPGe, the Tesla consumes the energy equivalent of one gallon of gasoline for every 134 miles. Converting MPGe to L/100km using the standard formula (235.215 divided by 134) gives an equivalent of 1.76 L/100km. The Prius at 57 MPG converts to 4.1 L/100km. Both are excellent by any standard, but the MPGe comparison makes the Tesla appear 2.3 times more efficient in energy terms, a figure that holds only because electricity delivers energy to wheels more efficiently than combustion. In Germany, Mia will see the Tesla rated at approximately 17 kWh/100km on European energy labels, not MPGe, which requires yet another conversion to understand.

Common Mistakes When Converting Fuel Economy Units

Assuming UK and US MPG are the same unit. Both countries call it "MPG." Both use miles in the numerator. The denominator differs: a US gallon is 3.785 litres; an Imperial gallon is 4.546 litres. A car quoted at 50 MPG in the British press achieves 41.6 MPG by US EPA standards. This 20% gap has tripped up international buyers, automotive journalists, and even professional fleet managers. Any time an MPG figure comes from a UK source, treat it as MPG(UK) and convert before comparing to a US figure.

Treating L/100km as a "higher is better" unit. Americans used to MPG sometimes interpret a car dropping from 8.0 L/100km to 7.0 L/100km as getting worse, because the number fell. It has actually improved: fewer litres consumed per 100 kilometres. When reading L/100km figures, reverse your instinct: celebrate when the number falls.

Multiplying MPG by a fixed number to get L/100km. This cannot work because MPG and L/100km are inverse (reciprocal) units. No single multiplication factor converts all MPG values to L/100km correctly. A 20 MPG car and a 40 MPG car need different factors (11.76 and 5.88 L/100km respectively). The only correct method is to divide the appropriate constant (235.215 for US, 282.481 for UK) by the MPG figure.

Comparing official test cycle figures across countries without adjustment. A car tested under the European WLTP cycle and one tested under the US EPA 5-cycle test will show different fuel economy figures even with identical engineering. WLTP figures tend to be 10 to 15 percent more optimistic than EPA figures for the same vehicle. UK WLTP figures and US EPA figures are tested differently and cannot be compared at face value. Convert both to L/100km as a common unit, then additionally note that real-world consumption typically runs 10 to 25 percent higher than any official test figure.

Converting km/L by multiplying by the miles-per-kilometre ratio. km/L and MPG are not simply connected by the miles-to-km ratio. The gallon-to-litre ratio also applies. To convert km/L to MPG(US): multiply by 2.352 (which accounts for both the 1.609 km/mile and the 3.785 L/US gallon conversions combined). Using only the 1.609 factor produces a result that is off by a factor of 2.352 divided by 1.609, a 46% error.