Home›Converters›Energy & Power›Fuel Efficiency Converter

Fuel Efficiency Converter

Energy & Power

Convert fuel efficiency between km/L, L/100km, and mpg instantly. Supports US and UK gallons — ideal for comparing Indian and international car mileage.

Reviewed by the thecalcu.com team · Last updated June 20, 2026

From
To

What is a Fuel Efficiency?

The Fuel Efficiency Converter translates fuel economy figures between km/L (kilometres per litre), L/100km (litres per 100 kilometres), mpg (miles per gallon, both US and UK gallon standards), and mi/L (miles per litre). Because these units express efficiency in fundamentally different directions, some measure distance per unit fuel, others measure fuel per unit distance, a straight multiplication doesn't work between all of them, and getting the math backwards is an easy mistake to make under time pressure. This tool exists for the exact moment when you're comparing a car's mileage spec from one country's brochure against another market's listing, or trying to make sense of a mpg figure when you've only ever thought in km/L.

Who Should Use This Fuel Efficiency Converter?

Car shoppers comparing international listings, say, an Indian buyer researching a US import, or a UK buyer eyeing a European model, need to translate mileage specs onto a familiar scale before the numbers mean anything. Automotive journalists and reviewers writing for a global audience regularly need to present the same efficiency figure in multiple units within a single article. Fleet managers overseeing vehicles sourced from different markets need consistent units to compare fuel costs across their fleet. Road trip planners crossing between countries with different fuel unit conventions can convert their car's known efficiency into whatever unit matches local fuel pricing. Students and researchers studying transportation efficiency data drawn from multiple countries' datasets need a reliable way to normalize units before analysis.

How to use this Fuel Efficiency calculator

  1. Select your source unit from the "from" dropdown, for example, "Kilometres per Litre (km/L)".
  2. Select your target unit from the "to" dropdown, for example, "Litres per 100 km (L/100km)".
  3. Enter your car's fuel efficiency figure in the input field.
  4. Read the converted value instantly as you type.
  5. If comparing a US listing to a UK one, double-check whether you need "Miles per Gallon, US" or "Miles per Gallon, UK", since the two differ by roughly 20%.
  6. Use the swap control to reverse direction if you need to go from mpg back to km/L or L/100km.

Formula & Methodology

Because km/L and mpg measure distance-per-fuel while L/100km measures fuel-per-distance, conversions between them use both multiplication and division steps depending on direction:

km/L to L/100km: L/100km = 100 / km/L
km/L to mpg (US): mpg = km/L × 2.352
km/L to mpg (UK): mpg = km/L × 2.825

Where the constants derive from combining kilometre-to-mile (1 km = 0.621371 mi) and litre-to-gallon (1 US gal = 3.785411784 L, 1 UK gal = 4.54609 L) conversion factors.

Worked example: Converting 15 km/L to L/100km and mpg (US):

L/100km = 100 / 15 = 6.67 L/100km
mpg (US) = 15 × 2.352 = 35.3 mpg

So a car rated at 15 km/L on an Indian spec sheet is roughly equivalent to 6.67 L/100km on a European scale or 35.3 mpg on a US scale.

What Insights Does This Converter Give You?

The reference conversion factors used here (2.352 for km/L to US mpg, 2.825 for km/L to UK mpg, and the inverse relationship for L/100km) come from exact, internationally standardized unit definitions, so precision isn't the limiting factor, context is. The biggest insight this tool surfaces is how differently the same real-world efficiency reads depending on which unit convention you're used to: a "low" number in L/100km (where lower is better) and a "high" number in mpg or km/L (where higher is better) can describe the identical car, and mixing up that directionality is the single most common error when comparing specs across markets.

Quick Reference

km/L L/100km mpg (US) mpg (UK)
10 10.0 23.5 28.2
15 6.67 35.3 42.4
20 5.0 47.0 56.5

For related conversions, see the Speed Converter for trip-time calculations, the Volume Converter if you're working with fuel tank capacity figures alongside efficiency numbers, or the Car Loan EMI Calculator if fuel economy is one factor in a broader car-buying budget.

Frequently Asked Questions

The two units measure fuel efficiency in inverted ways, mpg is distance per unit of fuel (higher is better), while L/100km is fuel used per unit of distance (lower is better). Because of this inverse relationship, the conversion between them isn't a simple multiplication, it involves a division step, which is exactly why a dedicated converter beats a rough mental estimate.
They use different gallon sizes, a US gallon is 3.785 litres while a UK (imperial) gallon is 4.546 litres, about 20% larger. The same car reported at 40 mpg in the UK would only be about 33 mpg on the US scale, so always confirm which mpg standard a figure refers to before comparing cars across markets.
Select 'Kilometres per Litre (km/L)' as your source unit and either 'Miles per Gallon, US' or 'Miles per Gallon, UK' as your target, depending on which market you're comparing against. Indian car brochures almost universally use km/L, so this conversion is the most common one for cross-market comparison shopping.
L/100km directly represents fuel cost per distance travelled, which maps more intuitively onto trip planning and fuel budgeting than a per-unit-fuel figure like mpg. It's the standard efficiency unit across most of the EU and several other markets that use the metric system for vehicle specs.
Lower is better for L/100km, since it represents fuel consumed per 100 km, a smaller number means the car uses less fuel to cover the same distance. This is the opposite direction from mpg and km/L, where higher numbers mean better efficiency, which is the single most common point of confusion when comparing specs across unit systems.
Most modern gasoline passenger cars fall somewhere between 15-25 km/L (roughly 35-60 mpg US, or 4.7-6.7 L/100km) depending on engine size, hybrid technology, and driving conditions. Larger SUVs and trucks typically run lower, while small hybrids can exceed 25 km/L.
No, this tool performs a pure unit conversion on whatever figure you enter, whether that's a city, highway, or combined rating. If you're converting a manufacturer's spec, make sure you're comparing the same driving condition (city, highway, or combined) on both sides.
Miles per litre is a hybrid unit sometimes used informally when someone measures distance in miles (common in the US and UK) but fuel in litres (common where fuel is sold by the litre), it's less standardized than mpg or km/L but appears often enough in casual conversation and older UK data to warrant its own conversion path.
The conversions are based on exact, published unit definitions (1 US gallon = 3.785411784 litres, 1 UK gallon = 4.54609 litres, 1 mile = 1.609344 km), so the math itself is exact. Any imprecision in your final comparison comes from the original fuel economy figures themselves, not from this conversion step.
Indirectly, yes, convert your car's efficiency rating into L/100km or mpg matching your fuel price unit, then multiply by your planned trip distance to estimate fuel needed. This converter handles the unit translation step; you'd still need to multiply by distance and local fuel price separately.
Also known as
km per litre to mpgmpg to kmplfuel economy converterlitres per 100km to mpgfuel consumption convertermiles per gallon converterl/100km converterkmpl to mpgcar fuel economy converterpetrol mileage converter