MPG to L/100km: How to Convert Fuel Economy Units

Converting MPG to L/100km is one of the most common fuel economy conversion challenges travelers face. Whether you are an American renting a car in Germany, a Brit comparing vehicles listed in European specs, or simply trying to make sense of a foreign car review, understanding how to move between miles per gallon and liters per 100 kilometers is essential for making informed decisions about fuel costs and vehicle efficiency.

The confusion is real. On Reddit communities like r/travel and r/AskEurope, travelers regularly post about the frustration of seeing fuel economy numbers that mean nothing to them. A rental car listing in France says "5.2 L/100km" and an American driver has no idea if that is good or terrible. This guide will make sure that never happens to you again.

The Three Major Fuel Economy Systems

Before diving into conversion formulas, it helps to understand why multiple systems exist in the first place. According to UnitConvr's guide on fuel economy, the world uses three primary ways to express how efficiently a vehicle uses fuel:

• MPG (Miles Per Gallon) — Used in the United States and the United Kingdom. Measures how many miles you can travel on one gallon of fuel. Higher is better. Critically, the US gallon (3.785 liters) and Imperial gallon (4.546 liters) are not the same—the Imperial gallon is roughly 20% larger.
• L/100km (Liters per 100 Kilometers) — The standard in continental Europe, Canada, Australia, New Zealand, and much of the rest of the world. Measures how many liters of fuel are consumed over 100 kilometers. Lower is better.
• km/L (Kilometers per Liter) — Common in parts of Asia (Japan, India) and some South American countries. Like MPG, higher numbers indicate better efficiency.

The most important thing to understand is the inverse relationship between MPG and L/100km. With MPG, a higher number means better efficiency. With L/100km, a lower number means better efficiency. This catches many people off guard because you cannot simply multiply or divide by a single constant—the conversion involves a reciprocal, as explained by Omni Calculator's fuel economy converter.

The "235 Shortcut" for Quick Conversions

If you only remember one thing from this article, make it this:

This shortcut (using the rounded constant 235 instead of the precise 235.215) is accurate enough for everyday use and is easy to do in your head. Standing at a rental car counter in Barcelona and the agent says the car gets 6 L/100km? Just divide: 235 ÷ 6 = about 39 MPG. That is excellent fuel economy.

The precise constant, as confirmed by CheckYourMath, is 235.215 for US gallons and 282.481 for Imperial gallons. For mental math, 235 and 282 work perfectly well.

Complete Conversion Formulas

For precise conversions, especially when comparing vehicles across different markets, here is a complete reference table. These formulas are consistent with those published by The Calculator Site and CheckYourMath:

Notice something in the table above: 30 US MPG and 36 Imperial MPG both come out to approximately the same L/100km value (around 7.84–7.85). That is because they represent the same actual fuel consumption—just measured with different-sized gallons. This is a critical distinction that trips up countless people, including seasoned automotive journalists.

The US vs. Imperial Gallon Trap

In most of Europe, fuel economy is measured in L/100km, making unit conversion essential for visiting drivers.

The difference between a US gallon and an Imperial gallon is not trivial. A US gallon is 3.785 liters, while an Imperial gallon is 4.546 liters—roughly 20% larger. This means the same car will always have a higher MPG number when measured in Imperial gallons than in US gallons, because each Imperial gallon contains more fuel.

Here is a real-world example that illustrates why this matters. Imagine you are reading a British car review that says a vehicle achieves 45 mpg. As an American, you might think that is similar to the 45 MPG your hybrid gets at home. But that 45 is Imperial MPG. Converting to US MPG: 45 ÷ 1.201 = 37.5 MPG (US). And converting to the metric standard: 282.481 ÷ 45 = 6.3 L/100km. All three numbers—45 Imperial MPG, 37.5 US MPG, and 6.3 L/100km—describe exactly the same fuel consumption. The FuelEconomy.gov site provides additional context on how these differences affect cross-market vehicle comparisons.

Quick Reference: MPG to L/100km Conversion Table

For fast lookups, here is a conversion table covering the most common MPG values. Keep this bookmarked for your next rental car trip abroad:

A general rule of thumb: anything under 6 L/100km (above roughly 39 US MPG) is considered excellent fuel economy for a conventional gasoline vehicle. Most compact cars in Europe sit in the 5–7 L/100km range, while SUVs and larger vehicles typically fall between 8–12 L/100km.

Why L/100km Can Actually Be More Intuitive

This might surprise American drivers, but L/100km has a mathematical advantage over MPG when it comes to understanding real-world fuel savings. Because MPG is a ratio with fuel in the denominator, improvements at the low end of the scale save far more fuel than the same improvement at the high end.

Consider two upgrades:

• Upgrading from 15 MPG to 20 MPG (a gain of 5 MPG) saves 1.67 gallons per 100 miles.
• Upgrading from 35 MPG to 40 MPG (also a gain of 5 MPG) saves only 0.36 gallons per 100 miles.

The same "5 MPG improvement" delivers 4.6 times more fuel savings in the first case. This is known as the "MPG illusion," and it is one reason researchers and fuel economy guides argue that a consumption-based metric like L/100km gives people a more accurate intuition about fuel costs. With L/100km, the savings scale linearly: going from 15.7 to 11.8 L/100km (a reduction of 3.9) represents a genuinely proportional improvement in fuel use.

Which Countries Use Which System

Knowing which measurement you will encounter at your destination helps you prepare. Here is a breakdown based on data from The Calculator Site:

• MPG (US) — United States
• MPG (Imperial) — United Kingdom (though L/100km is increasingly used alongside it)
• L/100km — European Union, Canada, Australia, New Zealand, South Africa, most of Latin America
• km/L — Japan, South Korea, India, Brazil, parts of Southeast Asia

If you are traveling to any country in the EU, Canada, or Australia, you will almost certainly encounter L/100km on rental car specs, fuel pump displays, and road signs. The 235 shortcut described above will be your best friend. Keep in mind that rental car brochures often show separate city and highway numbers—our guide on highway vs city MPG explains why those numbers differ so much and which one to use for your trip estimate.

Tips for Travelers Renting Cars Abroad

Based on advice shared across r/travel and r/AskEurope, here are practical tips for dealing with unfamiliar fuel economy units when renting abroad:

1. Screenshot the conversion table above. Having a quick reference on your phone eliminates guesswork at the rental counter or fuel station.
2. Remember that fuel is sold by the liter in most countries. When comparing prices, multiply the per-liter cost by 3.785 to get the rough equivalent of a US gallon price. European fuel is typically 2–3 times more expensive per gallon than in the US.
3. Choose a smaller car than you think you need. European parking spaces and roads are often narrower than American ones, and a compact car at 5–6 L/100km will save significantly on fuel compared to an SUV at 9–11 L/100km.
4. Ask the rental agent for the car's rated L/100km. This gives you a baseline to estimate fuel costs for your trip. Multiply L/100km by total kilometers, then divide by 100, to estimate total liters needed.
5. Switch the dashboard display to L/100km. Most modern cars let you toggle between unit systems in the settings menu. Using the local unit helps you build intuition as you drive.

Frequently Asked Questions