How to use Fuel Economy Converter
- Enter the Value you have, for example 45 for a car rated in mpg US.
- Choose Convert from, such as Miles per US gallon (mpg US).
- Choose Convert to, such as Liters per 100 kilometers (L/100 km).
- Leave Decimal places at 2, or pick another precision.
- The result, the km/L row and the direction note update as you change the values.
Example: Fuel Economy Converter
Convert miles per US gallon to liters per 100 kilometers.
Options
- Convert to
- Miles per gallon, km per liter and liters per 100 km all appear as their own units. US and imperial gallons are separate lines because they are different sizes.
- Decimal places
- Sets display rounding to 0, 2, 4, 6 or 8 places. The conversion itself runs on the full precision value, so only the printed figure is rounded.
Supported inputs and limits
Where your input is processed
This tool processes your input in this browser. Your text and files are not uploaded to UseFreeTools. Check this tool's limits for anything it may save on your device.
Why the reciprocal needs its own handling
Most converters divide one unit factor by another, which fails here because liters per 100 km is not a multiple of miles per gallon. The tool reads every entry into kilometers per liter first, inverting the volume-per-distance units, and then writes the answer in the target unit. That route keeps 45 mpg US at about 19.13 km/L and 5.23 L/100 km at the same time, and it lets one form handle both directions without a hidden second mode.
NIST Special Publication 811, Appendix B.8: mile and gallon factors
The two gallons behind the two mpg figures
A US liquid gallon is exactly 231 cubic inches, which is 3.785411784 L. An imperial gallon is exactly 4.54609 L, about a fifth larger. Because miles per gallon divides a distance by a volume, the same car records a bigger number on the imperial scale, near 1.20095 times the US figure. Both entries are named in full on the form so a figure is never read against the wrong gallon.
NIST Special Publication 811, Appendix B.8: US and imperial gallon factors
Questions about Fuel Economy Converter
Why does a higher mpg give a lower L/100 km?
One figure measures distance per unit of fuel and the other measures fuel per unit of distance, so they are reciprocals. A car that covers more miles on a gallon also needs fewer liters for every 100 kilometers.
Which gallon does mpg US use?
The US liquid gallon of 3.785411784 L, which is 231 cubic inches. An imperial gallon is 4.54609 L, so the same car reads about 20 percent higher in imperial mpg. The two are listed as separate units.
How is 1 mpg US related to US gallons per 100 miles?
They describe the same car. At one mile per gallon, 100 miles take 100 gallons, so 1 mpg US is exactly 100 US gallons per 100 miles.
Can I enter zero?
Zero is accepted in the distance per volume units and gives zero km/L. It has no finite reading in the consumption units, because no fuel for any distance is not a rate, and a consumption of zero liters is rejected.
Does this predict my real fuel use?
No. It converts a figure you already have. Real consumption depends on the route, speed, load, temperature and driving style, so treat a converted figure as a unit change rather than a forecast.