Fuel Economy Converter

How to use the fuel economy converter

1. Type the amount you want to convert.
2. Choose the unit you have and the unit you want.
3. Read the result, or use the table showing all 5 units at once.

Convert MPG, L/100 km and km/L

Fuel economy is expressed in several different ways depending on the country. The most common are miles per gallon (MPG), litres per 100 kilometres (L/100 km), and kilometres per litre (km/L).

MPG and km/L measure how far a vehicle travels on a fixed amount of fuel, while L/100 km measures how much fuel is needed to travel a fixed distance. That is the difference that catches people out: higher MPG and higher km/L mean better economy, while lower L/100 km means better economy. Converting between the two kinds inverts the number rather than scaling it.

The second trap is the gallon. A US gallon is 3.785411784 litres and an imperial gallon is 4.54609, so a UK MPG figure is about 20% higher than the US figure for exactly the same car.

Fuel economy conversion chart

Every figure below is produced by the converter above, so the chart and the tool cannot disagree.

MPG to L/100 km

To convert miles per US gallon into litres per 100 km, divide 235.215 by the MPG figure. The constant is the number of miles per gallon that corresponds to one litre per 100 km, and the division is what makes the relationship inverse: as one number rises the other falls.

• 20 MPG (US) is 11.76 L/100 km.
• 25 MPG (US) is 9.41 L/100 km.
• 30 MPG (US) is 7.84 L/100 km.
• 35 MPG (US) is 6.72 L/100 km.
• 40 MPG (US) is 5.88 L/100 km.
• 50 MPG (US) is 4.70 L/100 km.

L/100 km to MPG

The conversion runs the same way in reverse — divide 235.215 by the L/100 km figure for US MPG, or 282.481 for imperial MPG. Both columns are given below, because a car quoted at 6 L/100 km is a 39 MPG car in America and a 47 MPG car in Britain.

• 4 L/100 km is 58.80 MPG (US), or 70.62 MPG (UK).
• 5 L/100 km is 47.04 MPG (US), or 56.50 MPG (UK).
• 6 L/100 km is 39.20 MPG (US), or 47.08 MPG (UK).
• 7 L/100 km is 33.60 MPG (US), or 40.35 MPG (UK).
• 8 L/100 km is 29.40 MPG (US), or 35.31 MPG (UK).
• 10 L/100 km is 23.52 MPG (US), or 28.25 MPG (UK).

km/L to MPG

Kilometres per litre and miles per gallon are the same kind of measure — distance per unit of fuel — so this conversion is a straight multiplication with no inversion. One km/L is about 2.352 US MPG, or 2.825 imperial MPG.

• 8 km/L is 18.82 MPG (US), or 22.60 MPG (UK).
• 10 km/L is 23.52 MPG (US), or 28.25 MPG (UK).
• 12 km/L is 28.23 MPG (US), or 33.90 MPG (UK).
• 15 km/L is 35.28 MPG (US), or 42.37 MPG (UK).
• 18 km/L is 42.34 MPG (US), or 50.85 MPG (UK).
• 20 km/L is 47.04 MPG (US), or 56.50 MPG (UK).

US MPG vs UK MPG

US MPG and UK MPG are not the same measurement, because the two gallons are different volumes. One US gallon is 3.785411784 litres; one imperial gallon is 4.54609 litres. The same car therefore travels about 20% further on an imperial gallon, and its UK figure looks correspondingly better.

A vehicle rated at 40 MPG in the UK is about 33.31 MPG in the US. In the other direction, a 30 MPG US car is about 36.03 MPG UK. Neither figure is wrong, and neither car is more efficient than the other — they are the same car measured with different gallons.

This is worth checking before comparing a car sold in both markets, or reading a review written on the other side of the Atlantic.

Is higher or lower fuel economy better?

It depends which measure you are reading, which is the single easiest place to make a mistake with these units.

Compare fuel economy between two cars

Convert both figures into the same unit before comparing them. Take a car rated at 30 MPG (US) and one rated at 7 L/100 km: the first works out at 7.84 L/100 km, so the second uses slightly less fuel over the same distance.

Comparing on L/100 km also makes the savings honest. Improving from 40 to 50 MPG saves about a litre per 100 km; improving from 15 to 20 MPG saves nearly four. The MPG gap looks the same and the fuel saved is not, which is why fuel consumption is regulated in L/100 km almost everywhere outside the United States.

Once the figures agree, the fuel cost calculator turns them into money — the number that usually prompted the comparison in the first place.

How the conversion works

Every unit here is defined against kilometres per litre, and conversion goes through that base: one multiplication to reach it, one to leave. The imperial units are exact rather than approximate, because a mile, a gallon and a litre all have exact definitions in SI terms.

Litres per 100 km is handled separately, since it is an inverse measure. Converting to or from it takes a reciprocal, which is why no single multiplier converts MPG to L/100 km and why a table of approximate factors gets it wrong at the ends of the range.

Common uses

• Comparing a European car quoted in L/100 km against a US car quoted in MPG.
• Checking a UK MPG figure against the US equivalent before buying.
• Converting a trip computer reading into the units you think in.

Frequently asked questions

What is 30 MPG in L/100 km?

30 MPG (US) is 7.84 L/100 km. If the 30 MPG figure is an imperial one, it is 9.42 L/100 km instead.

What is 40 MPG in L/100 km?

40 MPG (US) is 5.88 L/100 km, and 40 MPG (UK) is 7.06 L/100 km. The gap between those two is the difference between the gallons, not between cars.

What is 5 L/100 km in MPG?

5 L/100 km is 47.04 MPG (US) or 56.50 MPG (UK). It is also 20.00 km/L.

How do you convert MPG to L/100 km?

Divide 235.215 by the US MPG figure, or 282.481 by an imperial one. The conversion is a division rather than a multiplication because the two units measure opposite things — distance per fuel against fuel per distance.

How do you convert L/100 km to MPG?

The same arithmetic in reverse: divide 235.215 by the L/100 km figure for US MPG, or 282.481 for imperial MPG. Because it is a reciprocal, the same improvement in L/100 km is worth more MPG at the efficient end of the range than at the thirsty end.

Is US MPG the same as UK MPG?

No. A US gallon is 3.785 litres and an imperial gallon is 4.546, so a UK figure is about 20% higher for the same car — 40 MPG UK is about 33.31 MPG US. Always check which gallon a figure refers to before comparing.

Is higher MPG better?

Yes. MPG measures how far you travel on a fixed amount of fuel, so more miles per gallon means less fuel for the same journey. The same applies to km/L.

Is lower L/100 km better?

Yes, and that is the reverse of MPG. L/100 km measures the fuel needed to cover a fixed distance, so a smaller number means a more efficient car. 5 L/100 km is better than 8.

What is km/L?

Kilometres per litre — how far a vehicle travels on one litre of fuel, used in Japan, India and much of South America. Higher is better, and one km/L is about 2.35 US MPG.

Does this work for diesel and petrol vehicles?

Yes. These are unit conversions, so they apply to any fuel, including LPG and the litres-per-100 km equivalents quoted for hybrids. What they cannot do is compare fuels by energy content — a litre of diesel holds more energy than a litre of petrol, which is part of why diesel figures look better.