Reading a metric spec sheet as an American driver
If you have ever looked at a Canadian brochure for the same car sold in the US, the fuel economy line looks broken. Where the American sticker says 33 mpg, the Canadian one says 7.1 L/100km. That is the same car and, give or take a test-cycle difference, the same efficiency. Canada, Mexico and the entire EU rate cars in liters per 100 kilometers, so anyone shopping across a border, importing a vehicle or reading a European road test needs this conversion.
The metric figure counts consumption rather than range. Instead of asking how far one gallon takes you, it asks how much fuel a fixed 100 km trip burns. Lower is better, which feels backwards at first. A car that goes from 25 to 35 mpg drops from 9.41 to 6.72 L/100km.
The formula, in US units
L/100km = 235.214583 ÷ MPG
That constant comes from the definition of the US gallon, 231 cubic inches, which works out to exactly 3.785411784 liters, combined with the mile at exactly 1.609344 km. Multiply 3.785411784 by 100 and divide by 1.609344 and you get 235.214583. The converter uses the full value, never a rounded 235.
American readers rarely need the imperial gallon, but if a figure comes from a British magazine, that gallon is 4.54609 liters and the constant becomes 282.480936. The US vs UK gallon guide explains why the two exist.
Worked example with an EPA rating
A full-size pickup with an EPA combined rating of 18 mpg: 235.214583 divided by 18 is 13.07 L/100km. A compact sedan at 33 mpg: 7.13 L/100km. A plug-in hybrid running on gasoline at 45 mpg: 5.23 L/100km.
Those three cars span the American market and they land at 13, 7 and 5 on the metric scale. Notice how the pickup's figure is not simply 'twice as bad' as the sedan; the reciprocal relationship squashes the good end of the scale and stretches the bad end.
Liters or litres
Liters is the American spelling and litres is the British and Canadian one. They are the same unit, defined as one cubic decimeter. This page uses the American form because it is written for readers who spell it that way; the main MPG to litres page uses the British form and is otherwise the same conversion. Search engines are told which page is the primary one, so the two never compete.
Things that go wrong
- Mixing up the EPA's three numbers. Window stickers show city, highway and combined. Convert the combined figure unless you specifically want one of the others.
- Assuming MPGe converts the same way. MPGe for electric cars is an energy-equivalence figure and does not describe liters of anything. It is deliberately not on this converter.
- Forgetting that older EPA ratings (before the 2008 method change) read higher than today's for the same car. A 1990s figure is not directly comparable.