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Fuel Efficiency

Convert between MPG (US/UK), L/100km, and km/L.

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Calculation Breakdown:

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About this topic

Miles per Gallon (MPG) Distance per unit of fuel (higher is better).

Used primarily in the US and UK, MPG measures how many miles a vehicle can travel on one gallon of fuel. Because US and UK gallons differ, the same car will have different MPG ratings in each.

Key formulas & rules

  • •Higher number = better efficiency
  • •US MPG uses 3.785L gallons
  • •UK MPG uses 4.546L gallons
  • •UK MPG is ~20% higher than US MPG
  • •Used for US and UK cars
  • •Easy to understand for consumers

Examples

Input Output Note
30 US MPG 36.2 UK MPG Conversion
50 UK MPG 41.3 US MPG Conversion
20 US MPG 11.8 L/100km To metric
30 US MPG 7.84 L/100km Efficient car

Real-world uses

Car window stickers Fuel cost calculations Fleet management
Liters per 100km (L/100km) Fuel per unit distance (lower is better).

Used in Europe, Canada, and many other regions, this metric measures how many liters of fuel are consumed to travel 100 kilometers. It is the inverse of MPG.

Key formulas & rules

  • •Lower number = better efficiency
  • •Inverse of distance per fuel
  • •Used in most metric countries
  • •Based on 100km distance
  • •Easier for calculating fuel usage
  • •Often paired with CO2 emissions

Examples

Input Output Note
5 L/100km 47 US MPG Very efficient
10 L/100km 23.5 US MPG Average
7.84 L/100km 30 US MPG Standard
15 L/100km 15.7 US MPG Inefficient

Real-world uses

European car specs Fuel cost estimates Emissions testing
Kilometers per Liter (km/L) Distance per unit of fuel in metric.

Common in Asia, South America, and parts of Europe, km/L is the metric equivalent of MPG. It measures how many kilometers a vehicle travels on one liter of fuel.

Key formulas & rules

  • •Higher number = better efficiency
  • •Easy to calculate for fuel purchases
  • •Common in Japan and India
  • •1 km/L = 2.352 US MPG
  • •Directly proportional to MPG
  • •Easy mental math

Examples

Input Output Note
15 km/L 35.3 US MPG Efficient
10 km/L 23.5 US MPG Average
20 km/L 47 US MPG Hybrid
5 km/L 11.8 US MPG Inefficient

Real-world uses

Asian car specs Fuel economy tracking Motorcycles

Modes & formulas

1

Fuel Efficiency Conversion

• Enter a value and choose the From and To units. • The calculator converts through km/L as the base unit. • L/100km uses a reciprocal formula (100 / value).
1 US MPG = 2.35215 km/L | 1 UK MPG = 2.82481 km/L

Because L/100km measures fuel per distance (the inverse of distance per fuel), converting to or from L/100km requires a reciprocal operation: L/100km = 100 / (km/L).

How to use it

Enter a value, choose From and To units, and click Convert. The result is shown with a one-click copy button.

Frequently asked questions

Why is L/100km inverted?
MPG measures distance per unit fuel, while L/100km measures fuel per unit distance. They're reciprocals of each other, so a higher MPG corresponds to a lower L/100km.
What's the difference between US and UK MPG?
A US gallon is 3.785 L, while a UK (imperial) gallon is 4.546 L. So the same MPG number means a different efficiency depending on which gallon is used.
What is MPG?
Miles per gallon. It measures how far a car can travel on one gallon of fuel.
What is L/100km?
Liters per 100 kilometers. It measures how much fuel is consumed to travel 100 kilometers.
Why is L/100km inverted compared to MPG?
MPG measures distance per unit of fuel. L/100km measures fuel per unit of distance. They are reciprocal metrics.
What is the difference between US and UK MPG?
A US gallon is 3.785 liters, while a UK gallon is 4.546 liters. Therefore, a car will get a higher MPG number in the UK.

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Read the full Fuel Efficiency guide — examples & 18 FAQs