⛽ Fuel Economy

Fuel Economy Converter

Compare a US window sticker, a UK brochure and a European spec sheet. Convert MPG, litres per 100 km and kilometres per litre. Press Convert to see the real figures.

Written and reviewed by SM Arijul Islam · Last reviewed 28 October 2026 · Editorial standards · Report an error

How fuel economy conversion works

Litres per 100 km measures fuel used, while MPG measures distance travelled. That means the relationship is inverted: doubling your MPG halves your litres per 100 km. This converter works internally in kilometres per litre, which makes every pairing consistent.

Formulas

L/100 km = 100 ÷ (km per litre)
MPG (US) = km per litre × 2.35215
MPG (UK) = km per litre × 2.82481
1 US gallon = 3.785411784 L · 1 imperial gallon = 4.54609 L
1 mile = 1.609344 km

US and UK gallons differ, so a US car showing 30 MPG is roughly 36 MPG by UK standards.

How to convert fuel economy

Fuel economy can be expressed in two opposite ways. Distance-per-volume measures such as miles per gallon and kilometres per litre say how far you travel on a fixed amount of fuel, so higher is better. Volume-per-distance measures such as litres per 100 kilometres say how much fuel a fixed trip consumes, so lower is better. Because the two are reciprocals, converting between them is not a simple multiplication — this converter applies the inverse relationship.

Common fuel economy conversions

One liters per 100 km expressed in other units of fuel economy
Unit	1 liters per 100 km equals
Kilometers per gallon (UK) (km/imp gal)	4.54609
Kilometers per gallon (US) (km/gal)	3.7854118
Miles per gallon (UK) (MPG (UK))	2.8248094
Miles per gallon (US) (MPG (US))	2.3521458
Kilometers per liter (km/L)	1
Miles per liter (mi/L)	0.62137119

Everyday uses

Comparing cars across different markets
Estimating the fuel cost of a trip
Understanding imported vehicle specifications
Eco-driving and efficiency tracking
Fleet reporting and emissions estimates

Real-world economy varies with speed, load, terrain and temperature. Official figures come from standardised test cycles.

Frequently asked questions

Why is lower better for L/100 km but higher better for mpg?

Because one measures fuel used per distance travelled and the other measures distance travelled per unit of fuel — they are reciprocal scales.

Is a US gallon the same as a UK gallon?

No. A US gallon is 3.785411784 L and a UK (imperial) gallon is 4.54609 L, so UK mpg figures look roughly 20% higher for the same car.

How do I compare 7 L/100 km with 40 mpg (US)?

Convert one to the other first. 7 L/100 km is about 33.6 mpg (US), so 40 mpg is the more economical figure.

Can I convert mpg to km/L directly?

Yes, they are both distance-per-volume, so a straight multiplication works — but any conversion involving L/100 km needs the inverse relationship.

More worked examples

30 US miles per gallon is about 7.84 litres per 100 km.
8 litres per 100 km is about 29.4 US miles per gallon.
30 UK miles per gallon is about 9.42 litres per 100 km, because the British gallon is larger.
A 100 km trip at 7 litres per 100 km uses exactly 7 litres of fuel.

US mpg to litres per 100 km

US miles per gallon converted to litres per 100 kilometres
US mpg	L/100 km
20 mpg	11.8 L/100 km
25 mpg	9.4 L/100 km
30 mpg	7.8 L/100 km
35 mpg	6.7 L/100 km
40 mpg	5.9 L/100 km
50 mpg	4.7 L/100 km

Common mistakes to avoid

Mixing US and UK gallons. A UK gallon is 4.546 litres against 3.785 in the US, so the same car appears about 20 percent more efficient in British figures.
Treating miles per gallon and litres per 100 km as proportional. They are inversely related, so better economy means a lower litres figure.
Using the wrong constant. The conversion to litres per 100 km uses about 235.215 for US gallons and 282.481 for UK gallons.
Assuming official figures match real driving. Lab test cycles are gentler than real traffic, so real economy is usually worse.

Further questions

Why do European figures measure fuel used instead of distance covered?

Litres per 100 km expresses consumption directly, while miles per gallon expresses distance. Both describe the same efficiency from opposite directions.

Which measure is more useful?

Litres per 100 km is linear, so it compares fuel saved more honestly. Going from 15 to 10 saves more than going from 5 to 4.

How do I convert km per litre to miles per gallon?

Multiply by about 2.352 for US miles per gallon, or 2.825 for UK miles per gallon.

Are published fuel economy figures realistic?

They are laboratory results from a standard test cycle, so they are useful for comparing cars but usually optimistic for everyday driving.

Sources and standards

Fuel economy can be written as distance per volume or volume per distance, and the two are reciprocal rather than proportional. This page uses the exact US gallon of 3.785411784 L and imperial gallon of 4.54609 L, so the mpg figures are not rounded approximations.