Fuel Consumption Converter (L/100km, MPG, km/L)
Convert vehicle fuel economy between L/100km, US MPG, UK MPG and km/L, and estimate trip cost.
Loading Fuel Consumption Converter (L/100km, MPG, km/L)… If nothing happens, please enable JavaScript.
Frequently asked questions
Is my data sent to a server?
What formulas are used?
Why are US MPG and UK MPG different for the same car?
When would I use this converter?
Why is L/100km described as 'reversed' compared to MPG?
What is a limitation of official fuel economy figures?
How do I interpret a fuel consumption figure — what is 'good'?
I am a new driver — why does my actual consumption differ from the manufacturer's claim?
Can this be used for commercial fleet planning?
What is a common mistake when comparing fuel economy?
Does the tool handle both litres and gallons for trip cost estimation?
About Fuel Consumption Converter (L/100km, MPG, km/L)
Fuel consumption is one of the most practically important specifications of any vehicle, yet it is reported in incompatible units depending on where in the world the car was sold or the data was published. Europe and most of the world uses litres per 100 kilometres (L/100km), a "consumption" metric where lower numbers indicate a more efficient car. The United States uses miles per US gallon (MPG), a "fuel economy" metric where higher numbers are better. The United Kingdom historically used miles per Imperial gallon, which is a larger unit than the US gallon, meaning the same physical car shows a higher MPG figure in UK tests than in US tests — a source of endless confusion for international car buyers and journalists. Many countries in Asia and Latin America use kilometres per litre (km/L), which is mathematically the inverse of L/100km. Because these units measure the same thing from different perspectives — fuel used per distance versus distance covered per fuel — converting between them requires division, not multiplication, which makes mental arithmetic tricky without a tool.
This converter is useful whenever you are comparing fuel economy data from different sources, planning a road trip and estimating fuel costs, evaluating a used car imported from another market, converting a manufacturer's claimed efficiency figure into familiar units, or simply trying to understand what a quoted MPG or L/100km figure means in practical terms. It is also helpful for comparing older and newer cars: European fleet averages fell from around 9 L/100km in the early 2000s to under 6 L/100km for modern efficient petrol cars, and understanding the percentage improvement requires working in consistent units.
All conversions and estimates run locally in your browser — no data is ever sent to a server. Enter a value in any of the four supported units and all others update automatically. The trip cost estimator multiplies your trip distance by the consumption rate and by your local fuel price per litre (or per gallon). Conversion formulas are exact: L/100km = 235.215 ÷ US MPG; UK MPG = US MPG × 1.20095 (Imperial gallon ÷ US gallon); km/L = 100 ÷ L/100km.
When interpreting official fuel economy figures, note that laboratory test results (WLTP in Europe, EPA in the US) are measured under controlled conditions and typically overstate real-world economy by 10–25%. Motorway driving at high speed, cold weather, air conditioning, roof boxes, and aggressive acceleration all increase fuel consumption significantly. For trip planning, add a 15–20% buffer to the official figure. These results are for informational and planning purposes only.
Miles, Litres, and Gallons: Why the World Cannot Agree on How to Measure Fuel Economy
The gallon has a surprisingly tangled history. The Imperial gallon was defined by the British Weights and Measures Act of 1824 as the volume of ten pounds of distilled water at 62°F — approximately 4.546 litres. The US gallon, however, traces its roots to the pre-1824 English "wine gallon" of 231 cubic inches (3.785 litres), a standard that American colonists brought with them and retained after independence. When Britain standardised its Imperial gallon in 1824, the United States had already been independent for nearly 50 years and did not follow suit. The result is two nations that both speak of "gallons" but mean measurably different things — a source of confusion in automotive, aviation, and agricultural contexts for two centuries.
The litres-per-100-kilometres standard emerged in continental Europe as part of a broader metrication effort in the 19th and 20th centuries. France, Germany, and their neighbours adopted the metric system far earlier than the UK or US, and L/100km became the natural automotive standard. When the European Economic Community (predecessor to the EU) began harmonising consumer information regulations in the 1970s and 1980s, L/100km was codified as the standard for vehicle fuel economy labelling across member states. The UK officially joined the metric system in many areas but retained MPG for road fuel economy on vehicle labels until 2010, when EU regulations finally required L/100km labelling — though MPG remained on labels alongside it for consumer familiarity.
The United States has considered adopting L/100km on multiple occasions, and the National Highway Traffic Safety Administration (NHTSA) and EPA have discussed it in the context of consumer comprehension research. Studies have shown that consumers make more rational fuel-saving decisions when information is presented in L/100km (or gallons-per-100-miles) rather than MPG, precisely because the linear scale of consumption metrics is easier to reason about than the reciprocal scale of economy metrics. Despite this, political resistance to metrication in the US has kept MPG on US window stickers, leaving the converter tool — and a fair amount of international confusion — as a practical necessity.