Use fuel economy to compare efficiency units.
Use this converter when vehicle ratings, trip reports, or markets express fuel efficiency in different systems. It translates the same efficiency among US MPG, imperial MPG, L/100 km, and km/L.
This tool does not estimate trip fuel or spending. After conversion, use Fuel Cost to apply the selected efficiency rating to a trip distance and fuel-unit price.
Cost, efficiency, energy, and power answer different questions.
Fuel Economy converts how efficiency is expressed and has no trip distance or price input. Fuel Cost estimates gasoline spending. EV Charging Cost estimates electricity expense, and EV Charging Time estimates ideal charging duration.
Formula and calculation method.
L/100 km = 235.214583 ÷ US MPG; imperial MPG = US MPG × 1.2009499255MPG and L/100 km move in opposite directions, so those conversions are reciprocal. US and imperial MPG also differ because a US gallon is 3.785411784 litres and an imperial gallon is 4.54609 litres.
See the transport decision, not just the math.
25 US MPG
Working: 235.214583 ÷ 25
Result: 9.41 L/100 km
Interpretation: A lower L/100 km result indicates less fuel consumed over the same 100 km.
7.5 L/100 km
Working: 235.214583 ÷ 7.5
Result: 31.36 US MPG
Interpretation: This is a US-gallon result; imperial MPG would be numerically higher.
20 km/L
Working: 100 ÷ 20
Result: 5 L/100 km
Interpretation: Both values describe the same consumption rate in different metric conventions.
Put the estimate in context.
Higher US MPG, imperial MPG, and km/L mean better efficiency. Lower L/100 km means better efficiency. Compare vehicles only after confirming the gallon standard and test cycle.
Display rounding can make an immediate reverse conversion differ slightly in the final decimal. The underlying reciprocal constants retain more precision than the displayed value.
Assumptions and common mistakes.
What the calculation assumes
- The selected MPG option determines whether the gallon is US or imperial.
- The input represents an average efficiency rate rather than one instantaneous reading.
- Conversions describe equivalent units and do not adjust for different laboratory test cycles.
- Displayed results round to two decimal places where needed.
Mistakes to avoid
- Assuming a higher L/100 km number means better efficiency.
- Mixing US MPG with imperial MPG.
- Treating MPG-to-L/100 km as a fixed multiplication instead of a reciprocal conversion.
- Using a converted rating as a prediction of real-world trip fuel consumption.
What unusual inputs mean.
Reciprocal fuel-economy conversion is undefined at zero, so the calculator returns an error.
The value is returned unchanged apart from display formatting.
They imply extremely high consumption in reciprocal units and are limited to keep output meaningful.
What this tool leaves out.
The converter does not compare regulatory test cycles, predict real-world efficiency, or account for driving conditions and vehicle load. It converts mathematical unit equivalents only; manufacturer ratings from different regions may not be directly comparable.
Automotive and energy questions.
How do I convert US MPG to L/100 km?
Divide 235.214583 by US MPG. For example, 25 US MPG is about 9.41 L/100 km.
Is lower L/100 km better?
Yes. L/100 km measures fuel consumed for a fixed distance, so a lower number means less fuel use.
Is US MPG the same as imperial MPG?
No. An imperial gallon is larger, so the same vehicle produces a higher imperial MPG number. Select the correct MPG standard before converting.
Why can’t fuel economy be zero?
These conversions use reciprocal division. A zero efficiency input would require division by zero and has no finite converted value.
Does converting a rating predict actual fuel use?
No. It preserves the unit-equivalent rate; real fuel use depends on route, weather, load, traffic, and driving style.