Use this mpg to l 100km converter to switch between US mpg, UK mpg, litres per 100 km.
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MPG to L/100km converter Convert US mpg, UK mpg, litres per 100 kilometres, and km/L instantly. This page also handles the reverse check when you need to turn L/100km back into mpg for an imported car review or a fuel-economy label.
Common presets
US and UK mpg are not interchangeable
A UK gallon is larger than a US gallon, so the same car always shows a higher mpg value in UK terms. If you are comparing reviews, labels, or owner reports, make sure you know which gallon the source used.
Gallon-size reference A US gallon is about 3.785 litres and a UK gallon is about 4.546 litres. For the same vehicle, UK mpg reads about 20.1% higher than US mpg, so the unit label matters before you compare a review, badge, or owner report.
Quick checkpoints
30 mpg (US) is about 7.84 L/100km and 12.75 km/L. Lower L/100km is better, while higher mpg and km/L are better.
Reverse conversion coverage
If you came here for l/100km to mpg, just switch the unit dropdown and enter the metric consumption figure. The calculator solves both directions using the same reciprocal relationship.
Enter a fuel economy figure Provide an mpg, km/L, or L/100km value to compare the four common efficiency units side by side.
MPG to L/100km converter: convert US mpg, UK mpg, km/L, and litres per 100km
Use this mpg to l 100km converter to switch between US mpg, UK mpg, km/L, and litres per 100 kilometres without guessing which number should go up or down. It is most useful when you are comparing an imported car review, an owner-reported mpg figure, a European fuel label, or a trip-planning estimate and need the same fuel economy expressed in one consistent unit.
How to convert mpg to L/100km and back
MPG and km/L rise as a vehicle becomes more efficient, but L/100km falls. That inverse relationship is why the conversion cannot be done by a simple one-to-one multiplier. The same car may look “better” in one system by showing a bigger number and “better” in another by showing a smaller number.
There is another complication: US mpg and UK mpg use different gallons. A UK gallon is larger than a US gallon, so any UK mpg figure for the same vehicle will always be higher than the US mpg figure.
That is why queries like convert mpg to l 100, mpg to liters per 100km, and l per 100km to mpg all need the same two checks first: which gallon standard is being used, and whether the source expresses efficiency as distance per unit of fuel or fuel used per fixed distance.
L/100km = 235.215 / mpg (US)
Relationship between US mpg and metric consumption.
L/100km = 282.481 / mpg (UK)
Relationship between UK mpg and metric consumption.
L/100km = 100 / (km/L)
Metric consumption and metric efficiency are reciprocal forms.
When each unit is most useful
Use mpg when you are matching an American or British review, older brochure, or owner discussion that already quotes distance per gallon. Use L/100km when you are matching European labels, fleet reporting, or trip-cost calculations based on litres consumed over a fixed route length.
km/L is often the easiest “plain-language” metric efficiency format because it answers how far one litre takes you. It is especially useful when you want an intuitive comparison without the inverse logic of L/100km.
For everyday driving-cost planning, L/100km often feels more practical because it connects directly to fuel purchased over a route. For forum discussion and spec-sheet comparisons, mpg is often more familiar. The calculator keeps all four views visible so you do not have to mentally flip the logic every time you change source.
Why the same car can look different across sources
A car rated at 30 mpg (US) is about 36.03 mpg (UK), around 12.75 km/L, and about 7.84 L/100km. Those are all the same efficiency, just expressed in different systems.
That is why an international car review, dealer sheet, and owner forum may appear to disagree when they are actually describing the same performance using different gallon sizes and consumption formats.
If one source uses UK mpg and another uses US mpg, the UK number will always look more flattering. If a third source uses litres per 100km, the “better” number becomes smaller rather than larger. Converting everything into one system removes that confusion immediately.
The unit difference is the main reason mpg to L/100km conversion feels confusing at first. A US gallon is about 3.785 litres, while a UK or imperial gallon is about 4.546 litres. For the same vehicle, that larger imperial gallon makes mpg (UK) read higher than mpg (US).
That also means a review that omits the gallon standard is incomplete. If you are comparing imported reviews, owner posts, or dealer sheets, confirm whether the original figure is US mpg or UK mpg before you decide that one car is more efficient than another.
The calculator keeps both mpg standards visible side by side so you can compare the source figure without doing a mental adjustment first.
1 US gallon ≈ 3.785 L
US gallon size used for MPG (US) conversions.
1 UK gallon ≈ 4.546 L
Imperial gallon size used for MPG (UK) conversions.
mpg (UK) reads higher than mpg (US)
The imperial gallon contains more fuel, so the distance-per-gallon number reads higher.
Common mpg to L/100km checks: 20, 25, 30, and 40 mpg
Common search queries often ask for benchmark conversions such as 20 mpg to l 100km, 25 mpg to l 100km, 30 mpg to l 100km, and 40 mpg to l 100km. In US terms, 20 mpg is about 11.76 L/100km, 25 mpg is about 9.41 L/100km, 30 mpg is about 7.84 L/100km, and 40 mpg is about 5.88 L/100km.
Those checkpoints are useful because they help you place a review figure quickly. Around 11 to 12 L/100km usually signals a relatively thirsty petrol vehicle or heavy SUV, around 7 to 8 L/100km looks more moderate, and under 6 L/100km starts to look notably efficient in conventional fuel-economy terms.
If the source uses UK mpg instead, the mpg number will be higher for the same vehicle. That is why 40 mpg (UK) is not the same as 40 mpg (US), and why converting the exact source value matters before you compare vehicles across regions.
Reverse checks for litres per 100 kilometres
The reverse queries matter just as much because many vehicle labels and European reviews start from litres per 100 kilometres instead of MPG. At the same benchmark points, 5 L/100km is about 47.0 mpg (US) and 56.5 mpg (UK), 6 L/100km is about 39.2 mpg (US) and 47.1 mpg (UK), 7 L/100km is about 33.6 mpg (US) and 40.4 mpg (UK), and 8 L/100km is about 29.4 mpg (US) and 35.3 mpg (UK).
Those reverse checks are especially useful when you are comparing a European fuel label against a forum post or import listing that only gives mpg. Converting back to MPG can make the number easier to compare at a glance, but the L/100km figure remains the better trip-cost format because it tells you fuel used per fixed distance.
If the original source value is already in L/100km, use that exact figure rather than rounding early. A small rounding difference can make a vehicle look slightly better or worse than it really is when you are comparing near-identical cars.
Why lower L/100km is better but higher mpg is better
MPG and km/L express efficiency as distance travelled from a unit of fuel, so a larger number is better. L/100km expresses consumption as fuel used over a fixed distance, so a smaller number is better. The vehicle is not changing; only the framing changes.
This is the main reason people find metric and imperial fuel-economy figures visually confusing. A better car should show a bigger number in one format and a smaller number in the other. The calculator solves that by showing the same vehicle in all four units at once.
If you are asking whether liters per 100km to mpg or mpg to liters per 100km is the easier direction, the answer is mostly about which unit you want to read afterward. The math works both ways because the relationship is reciprocal.
How this helps with trip planning and fuel cost
L/100km is often the easiest format for estimating trip fuel use because it tells you directly how many litres a vehicle burns over 100 kilometres. If a car uses 6 L/100km, then a 500 km journey is roughly 30 litres before traffic, weather, and load differences.
MPG can still be useful for owner forums and local fuel labels, but it is less intuitive for quick route budgeting because the relationship is inverted. That is one reason many trip-planning and fleet-reporting tools prefer litres-per-distance reporting.
For the most practical comparison workflow, convert the rating into one unit, then pair it with a trip distance or fuel price calculator. That keeps fuel-economy discussion and fuel-cost planning aligned instead of mixing two incompatible ways of reading the same efficiency.
Frequently asked questions
Is lower L/100km better?
Yes. L/100km measures how much fuel the vehicle uses over a fixed distance, so a lower number means better efficiency.
Why is UK mpg higher than US mpg?
Because the UK gallon is larger than the US gallon. The vehicle travels the same distance, but the gallon unit itself contains more fuel in UK terms.
Why does km/L appear in this converter too?
Because many people prefer to read fuel economy as distance per litre rather than fuel used per 100 km. km/L and L/100km are both common metric expressions of the same efficiency.
Can I compare international car specs directly after conversion?
Yes, as long as you account for the unit system. After converting to the same unit, you can make a like-for-like comparison more easily.
How do you convert mpg to L/100km?
For US mpg, divide 235.215 by the mpg figure. For UK mpg, divide 282.481 by the mpg figure. The difference exists because the UK gallon is larger than the US gallon.
How do you convert L/100km to mpg?
Reverse the relationship by dividing the relevant constant by the L/100km figure. US mpg equals 235.215 divided by L/100km, while UK mpg equals 282.481 divided by L/100km.
What is 30 mpg in L/100km?
Thirty mpg (US) is about 7.84 L/100km. Thirty mpg (UK) is about 9.42 L/100km if you are converting from an imperial-gallon source, so you should always check whether the original mpg value is US or UK.
What is 20 mpg in L/100km?
Twenty mpg (US) is about 11.76 L/100km. That is a useful benchmark because it gives a quick sense of how rapidly consumption rises as mpg falls.
Can I use this for UK mpg as well as US mpg?
Yes. This page supports both gallon standards directly, which is essential because UK mpg and US mpg are not interchangeable. If the source is British, use UK mpg. If it is American, use US mpg.
Is km/L the same as L/100km?
They describe the same fuel economy in two different metric formats. km/L tells you how far one litre takes you, while L/100km tells you how much fuel is used over a fixed 100-kilometre distance.
Which fuel-economy unit is best for trip cost planning?
L/100km is often the easiest because it ties directly to fuel consumed over a fixed route distance. That makes it simpler to estimate how many litres you will buy over a journey, especially when fuel prices are quoted per litre.
Why do imported car reviews and local labels seem to disagree?
They may be using different gallon standards or a different measurement style entirely. One source may use US mpg, another UK mpg, and another litres per 100 kilometres. The vehicle can be identical while the numbers look very different.
How much higher is mpg (UK) than mpg (US) for the same car?
For the same vehicle, mpg (UK) is about 20% higher than mpg (US) because the imperial gallon is larger. The exact difference depends on the same underlying efficiency figure, but the unit gap is always large enough that you should not compare the two numbers directly without converting them first.
What is 25 mpg in L/100km?
Twenty-five mpg (US) is about 9.41 L/100km. If the source is using UK mpg instead, the same vehicle would show a higher mpg number and a different L/100km result, so check the gallon standard before comparing vehicles.
What is 40 mpg in L/100km?
Forty mpg (US) is about 5.88 L/100km. Forty mpg (UK) is not the same figure because the imperial gallon is larger, so the same car will appear more efficient in UK mpg terms than in US mpg terms.
Should I compare fuel economy using mpg, km/L, or L/100km?
Use the unit that matches the source first, then convert everything into one system before you compare cars. L/100km is often the easiest for trip-cost planning, mpg is common in North American and British review copy, and km/L is a useful metric bridge when you want a distance-per-fuel view.
