Fuel Economy Converter

Convert fuel economy between US MPG, UK MPG, km per liter and L/100km — essential when comparing cars across regions.

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Quick answer

Fuel Economy is a free, private online tool that lets you convert fuel economy between US MPG, UK MPG, kilometers per liter and liters per 100km. It runs entirely in your browser, so nothing you enter is uploaded to a server.

How to use the Fuel Economy

Enter the number you want to convert in the Value field.
Pick the unit you're converting From and the unit you want To.
Read the converted result, or use ⇅ to swap the two units.
Check the All units table to see your value expressed in every supported unit at once.

Privacy: this tool runs entirely in your browser. Your input is never sent to, received by, or stored on any server — there are no uploads and no tracking of what you enter.

About Fuel Economy

Different systems

The US and UK both use miles per gallon but their gallons differ. Europe uses L/100km (lower is better) and some places use km/L.

Why it is not linear

L/100km is an inverse measure — as efficiency rises, the number falls — so converting needs care, which this tool handles for you.

Where it helps

Comparing car specs from different countries and planning fuel costs for a trip.

Frequently asked questions

Is US MPG the same as UK MPG?

No — the UK gallon is larger, so UK MPG figures look higher for the same car.

What does L/100km mean?

Liters of fuel used per 100 km; lower numbers are more efficient.

How do I convert MPG to L/100km?

This tool does it automatically since the relationship is inverse.

Understanding Fuel Economy in depth

Why fuel economy is tricky to convert

Fuel economy describes how far a vehicle travels on a given amount of fuel, but countries express it in fundamentally different — and sometimes inverted — ways. The US and UK use miles per gallon (higher is better), while much of the world uses litres per 100 km (lower is better). Because one is distance-per-fuel and the other fuel-per-distance, converting is not a simple multiply.

US versus UK MPG

Both the US and UK quote 'miles per gallon', but their gallons differ: a UK gallon (4.546 L) is about 20% larger than a US gallon (3.785 L). So the same car shows a higher MPG figure in UK terms than in US terms. Comparing a US and UK review of the same vehicle without converting gives a misleading picture — this tool keeps them distinct.

How the conversion works

Because L/100 km is an inverse measure, the tool converts through a common reference (kilometres per litre) and inverts where needed, rather than applying a single factor. That means you can move freely between US MPG, UK MPG, km/L and L/100 km and always get the mathematically correct result.

Reading the numbers

With MPG, bigger means more efficient. With L/100 km, smaller means more efficient — a car using 5 L/100 km is thriftier than one using 8. A rough anchor: 40 US MPG is about 5.9 L/100 km. Knowing which direction 'better' runs in each system prevents costly misjudgements when buying or comparing cars.

Everyday uses

Compare car specs across regions, plan fuel costs for a trip, and understand efficiency figures in adverts and reviews written for another market. Everything runs locally in your browser.