To turn miles per gallon into liters per 100 kilometers, divide a fixed number by the MPG figure: 235.21 for US gallons, or 282.48 for imperial (UK) gallons. The two numbers differ because the two gallons do. The conversion is a division, not a multiplication, because the units measure opposite things: MPG is distance per fuel, while L/100 km is fuel per distance. That inversion also explains why MPG figures often mislead people about how much fuel they will actually save. This guide covers the formula, both gallons, conversion tables, worked examples, and how electric-car ratings (MPGe) fit in.

Curve of US gallons used over 10,000 miles against miles per gallon, falling steeply from 1,000 gallons at 10 mpg and flattening toward 167 gallons at 60 mpg. An 18 to 28 mpg upgrade saves 198 gallons, while 34 to 50 mpg saves only 94
Chart: fuel used over 10,000 miles at each MPG rating. Raising a low MPG figure saves far more fuel than the same-looking jump at the high end.

Where 235.21 and 282.48 come from

The constants are just unit definitions combined. A mile is exactly 1.609344 km. A US liquid gallon is exactly 231 cubic inches, which is 3.785411784 liters. An imperial gallon is exactly 4.54609 liters. So:

Which gallon is your MPG?

This matters more than any rounding. The imperial gallon is about 20% larger than the US gallon, so the same car gets a UK figure about 20% higher. A rule that works:

If a source doesn't say which gallon, check where it was published. Comparing a UK 50 mpg with a US 50 mpg is comparing 5.65 L/100 km with 4.70 L/100 km. The fact that the United States and Britain kept different gallons, and only partly moved to metric, is covered in our guide to metric and imperial around the world.

Two blocks drawn to scale: the US gallon of 3.785411784 liters and the larger imperial gallon of 4.54609 liters
Diagram: the imperial gallon holds 1.2009 times as much as the US gallon.

MPG to L/100 km conversion table

All values computed from the exact definitions and rounded to two decimals. The last column, US gallons per 100 miles, is the consumption figure the EPA label also shows.

MPGL/100 km (US mpg)L/100 km (UK mpg)km/L (US mpg)US gal / 100 mi
1023.5228.254.2510.00
1515.6818.836.386.67
2011.7614.128.505.00
259.4111.3010.634.00
307.849.4212.753.33
356.728.0714.882.86
405.887.0617.012.50
455.236.2819.132.22
504.705.6521.262.00
603.924.7125.511.67
703.364.0429.761.43

For context, the EPA reported that new US vehicles averaged a record 27.1 mpg in model year 2023, which is 8.68 L/100 km.

Worked examples

1. A US rating to metric and UK figures

A US car is rated 30 mpg combined.

  1. L/100 km: 235.215 ÷ 30 = 7.84 L/100 km.
  2. UK mpg: 30 × 1.20095 = 36.0 UK mpg.
  3. km/L: 100 ÷ 7.84 = 12.75 km/L.

2. A European figure to US and UK mpg

A European spec sheet says 5.5 L/100 km.

  1. US mpg: 235.215 ÷ 5.5 = 42.8 US mpg.
  2. UK mpg: 282.481 ÷ 5.5 = 51.4 UK mpg.
  3. Same car, same fuel use: the 8.6 mpg gap is only the gallon.

3. Which upgrade saves more fuel?

This is the example from Richard Larrick and Jack Soll of Duke University, published in Science in 2008. Over 10,000 miles, compare replacing an 18 mpg vehicle with a 28 mpg one against replacing a 34 mpg car with a 50 mpg one.

  1. 18 mpg: 10,000 ÷ 18 = 555.6 gallons. 28 mpg: 10,000 ÷ 28 = 357.1 gallons. Saving: 198 gallons.
  2. 34 mpg: 10,000 ÷ 34 = 294.1 gallons. 50 mpg: 10,000 ÷ 50 = 200.0 gallons. Saving: 94 gallons.
  3. The 10 mpg improvement saves more than twice as much fuel as the 16 mpg one.

Most people in their study picked the 34 to 50 mpg upgrade as the bigger saving. The authors called this the "MPG illusion" and suggested stating efficiency as gallons per distance driven instead.

Odd but true: 10 to 20 mpg beats 30 to 40 mpg by a factor of six

Going from 10 to 20 mpg cuts consumption by 11.76 L/100 km (500 US gallons per 10,000 miles). Going from 30 to 40 mpg cuts only 1.96 L/100 km (83 gallons). Both are "+10 mpg", but fuel use follows the reciprocal, so the gains shrink fast as MPG rises.

Why L/100 km is linear and MPG is not

Fuel used on a trip is distance × consumption. With L/100 km, that is a straight multiplication: a car at 8 L/100 km uses exactly twice the fuel of one at 4 L/100 km over any distance, and fuel cost scales the same way at a fixed price. With MPG, fuel used is distance ÷ mpg, so equal steps in MPG translate into smaller and smaller savings. That is the shape of the curves in both charts: steep at low MPG, nearly flat at high MPG.

Two falling curves of liters per 100 km against miles per gallon from 10 to 70, one for US gallons and a higher one for UK gallons. At 30 mpg the US curve is at 7.84 and the UK curve at 9.42 L/100 km
Chart: L/100 km against MPG for both gallons. The UK curve sits 20% higher because each UK gallon holds 20% more fuel.

The US EPA label now shows a gallons-per-100-miles figure next to MPG for the same reason. Comparing cars in L/100 km (or gallons per 100 miles) gives the right answer directly. When you compare two cars, convert both to consumption first, then subtract.

Electric cars: MPGe and kWh per 100 miles

An electric car burns no gallons, so the EPA rates it in miles per gallon of gasoline equivalent (MPGe), introduced on the window sticker in November 2010. The EPA treats 33.7 kWh of electricity as equal in energy to one US gallon of gasoline. MPGe is therefore miles driven per 33.7 kWh.

The EPA label also shows the consumption figure in kilowatt-hours per 100 miles, which is the more useful number for estimating charging cost. Converting is the same reciprocal trick:

Example: a car rated 120 MPGe uses 3,370 ÷ 120 = 28.1 kWh/100 mi, or 2,094 ÷ 120 = 17.5 kWh/100 km. The table below gives a few more values, computed from the EPA's 33.7 kWh figure.

MPGekWh/100 mikWh/100 km
80 MPGe42.126.2
100 MPGe33.720.9
120 MPGe28.117.5
140 MPGe24.115.0

Note that kWh/100 km measures energy per distance, not fuel volume, so it cannot be compared directly with L/100 km without an energy-equivalence assumption like the EPA's.

Using the SamemaS fuel economy converter

The fuel economy converter shows L/100 km, km/L, US mpg, UK mpg, liters per mile, mL/km and km per US gallon together. Type into any field and the others update in your browser, using the 235.215 and 282.481 constants above. It has no MPGe or kWh field, so use the two formulas in the previous section for electric cars, or the energy converter if you need kWh in other units.

The short version

Frequently asked questions

1How do I convert MPG to L/100 km?
Divide 235.215 by the US mpg figure, or 282.481 by the UK (imperial) mpg figure. For example, 30 US mpg is 235.215 ÷ 30 = 7.84 L/100 km. The same formula works in reverse: mpg = 235.215 ÷ L/100 km.
2Why is UK MPG higher than US MPG for the same car?
The imperial gallon is 4.54609 liters and the US gallon is 3.785411784 liters, so a UK gallon holds 1.20095 times as much fuel. The same car therefore travels about 20% farther per UK gallon, and its UK mpg figure is about 20% higher.
3Why is L/100 km better for comparing cars?
Fuel used is distance times L/100 km, so savings are a simple subtraction. With MPG, fuel used is distance divided by MPG, so equal MPG gains save less and less fuel. Over 10,000 miles, 18 to 28 mpg saves 198 US gallons while 34 to 50 mpg saves only 94.
4What does MPGe mean?
Miles per gallon of gasoline equivalent. The US EPA treats 33.7 kWh of electricity as equal in energy to one gallon of gasoline, so MPGe is miles per 33.7 kWh. To get kWh per 100 miles, divide 3,370 by the MPGe figure: 120 MPGe is 28.1 kWh/100 mi.

Sources

  1. Gallon — Wikipedia
  2. Miles per gallon gasoline equivalent — Wikipedia
  3. What Is MPGe, and How Is It Derived? — AAA Club Alliance
  4. Gallons Per Mile Would Help Car Shoppers Make Better Decisions — Duke University Fuqua School of Business
  5. EPA Report Shows US Fuel Economy Hits Record High and CO2 Emissions Reach a Record Low — US Environmental Protection Agency
  6. Understanding fuel consumption ratings — Natural Resources Canada