MPG to L/100km Converter
Instantly convert between miles per gallon (US and UK), liters per 100 kilometers, and kilometers per liter. Enter a value in any fuel efficiency unit and see all four conversions at once, with an efficiency rating and comparison to average vehicles in the US, UK, and Europe.
How the Fuel Efficiency Converter Works
Fuel efficiency is measured differently around the world, which creates confusion when comparing vehicles across markets, reading international car reviews, or calculating fuel costs while traveling abroad. The United States uses miles per gallon based on the US gallon (3.785 liters), the United Kingdom uses miles per gallon based on the larger imperial gallon (4.546 liters), most of Europe and Australia use liters per 100 kilometers, and Japan uses kilometers per liter. This converter handles all four units seamlessly, allowing you to enter a value in whichever system you know and instantly see the equivalent in all other systems.
The mathematical relationship between these units involves inverse proportions that are not intuitively obvious. MPG and km/L are "higher is better" metrics where a larger number means more efficient. In contrast, L/100km is a "lower is better" metric where a smaller number indicates better efficiency. The conversion factor between US MPG and L/100km is 235.215 — divide this constant by the MPG value to get L/100km, or divide by L/100km to get MPG. For UK MPG, the conversion factor is 282.481 because the imperial gallon is approximately 20% larger than the US gallon. This means a UK MPG figure is always higher than the US MPG figure for the same vehicle, which often leads to confusion when comparing specifications from different markets.
Understanding fuel efficiency ratings in context is equally important. What constitutes "good" fuel economy varies by vehicle class and market standards. In the United States, the average new passenger car achieves about 36 MPG (US) combined, while the average light truck or SUV gets about 28 MPG. In Europe, where fuel is more expensive and vehicles tend to be smaller, the average new car achieves about 5.5-6.5 L/100km (36-43 MPG US equivalent). The most efficient non-hybrid petrol cars on the market achieve around 4-5 L/100km (47-59 MPG US), while hybrid vehicles routinely achieve 3.5-4.5 L/100km (52-67 MPG US). These benchmarks help you evaluate whether your vehicle is performing well relative to its class and segment.
Conversion Formulas
L/100km = 235.215 ÷ MPG (US)
L/100km = 282.481 ÷ MPG (UK)
km/L = 100 ÷ L/100km
MPG (US) = MPG (UK) × 0.8327
Where:
- 235.215 = conversion constant for US gallons (3.78541 L) and miles (1.60934 km)
- 282.481 = conversion constant for UK imperial gallons (4.54609 L) and miles
- 0.8327 = ratio of US gallon to UK gallon
Understanding the Different Measurement Systems
US MPG vs UK MPG — Why the Difference Matters
One of the most common sources of confusion is the difference between US and UK miles per gallon. Both countries use miles and gallons, but the gallons are different sizes. The US gallon equals 3.785 liters while the UK imperial gallon equals 4.546 liters — roughly 20% larger. This means a car rated at 40 MPG in the UK would only achieve about 33 MPG using US measurements, even though the actual fuel consumption is identical. When reading car reviews or specifications from another country, always check which gallon system is being used. A quick test: if the MPG figure seems surprisingly high for a non-hybrid vehicle (above 50-60 MPG), it is likely using UK imperial gallons.
L/100km — The Most Logical System
Many automotive engineers and fuel economy experts consider liters per 100 kilometers to be the most practical measurement system because it directly tells you how much fuel a journey will consume. If your car uses 7 L/100km and you are driving 300 km, you simply calculate 3 times 7 equals 21 liters of fuel needed. With MPG, the same calculation requires division, which is less intuitive. Additionally, L/100km scales linearly — improving from 10 to 8 L/100km saves the same absolute amount of fuel as improving from 6 to 4 L/100km over the same distance. With MPG, the relationship is nonlinear, meaning that improving from 15 to 20 MPG actually saves more fuel than improving from 35 to 50 MPG over the same distance, which is counterintuitive but mathematically correct.
Efficiency Ratings by Vehicle Class
Fuel Efficiency Benchmarks
- Excellent: Below 5 L/100km (above 47 MPG US) — hybrids, small efficient cars
- Good: 5-7 L/100km (34-47 MPG US) — compact to midsize sedans
- Average: 7-10 L/100km (24-34 MPG US) — larger sedans, small SUVs
- Poor: Above 10 L/100km (below 24 MPG US) — large SUVs, trucks, performance cars
Practical Applications
Fuel efficiency conversions are essential for several common scenarios. International travelers renting cars abroad need to compare quoted consumption figures against familiar benchmarks. Car buyers comparing models across markets need accurate conversions to make fair comparisons. Automotive journalists and reviewers frequently need to translate between systems for international audiences. Fleet managers operating vehicles across multiple countries need standardized efficiency data for budgeting and reporting. This converter eliminates the guesswork by providing all four major units simultaneously, along with a qualitative efficiency rating that puts the number in practical context regardless of which unit you are most familiar with.
Frequently Asked Questions
How do I convert MPG to L/100km?
To convert US MPG to L/100km, divide 235.215 by the MPG value. For example, 30 MPG (US) equals 235.215 / 30 = 7.84 L/100km. To convert UK (imperial) MPG to L/100km, divide 282.481 by the MPG value. For example, 40 MPG (UK) equals 282.481 / 40 = 7.06 L/100km. The constants differ because the US gallon (3.785 L) is smaller than the UK imperial gallon (4.546 L).
Why is UK MPG higher than US MPG for the same car?
UK MPG figures are always about 20% higher than US MPG figures for the same vehicle because the UK imperial gallon is larger (4.546 liters vs 3.785 liters for the US gallon). A car that travels 30 miles on a US gallon would travel the same 30 miles on a UK gallon — but since the UK gallon contains more fuel, you would also get an additional 6 miles from the extra fuel. So the same car would be rated at 30 MPG (US) but 36 MPG (UK). Always check which system is being used when comparing MPG figures.
What is considered good fuel efficiency in L/100km?
For passenger cars, below 5 L/100km is excellent (typical of hybrids and small efficient cars), 5-7 L/100km is good (compact to midsize sedans), 7-10 L/100km is average (larger sedans and small SUVs), and above 10 L/100km is poor (large SUVs, trucks, and performance vehicles). The EU fleet average target for new cars is approximately 4.1 L/100km equivalent (95 g CO2/km), which reflects a push toward very efficient vehicles including hybrids and plug-in hybrids.
Why is L/100km considered better than MPG for fuel calculations?
L/100km is more practical for trip planning because it directly tells you fuel consumption per distance. If your car uses 8 L/100km and you drive 400 km, you need exactly 32 liters. L/100km also scales linearly — saving 2 L/100km always saves the same amount of fuel regardless of the starting point. MPG has a nonlinear relationship where improving from 10 to 15 MPG saves more fuel than improving from 30 to 50 MPG over the same distance, which is counterintuitive and can lead to poor decision-making about vehicle choices.
How do I find my car's real fuel consumption?
The most accurate method is the tank-to-tank calculation: fill your tank completely, reset your trip odometer, drive normally until you need fuel again, fill up completely, and divide the liters added by the kilometers driven (then multiply by 100 for L/100km). Repeat this over several tanks for a reliable average. Most modern cars also display instantaneous and average fuel consumption on the dashboard computer, though these readings can be 5-10% optimistic compared to actual measured consumption. Using the manual fill-up method over at least 3-4 tanks gives the most reliable real-world figure.