Fuel economy converter
Convert litres per 100 kilometres, kilometres per litre and US or imperial miles per gallon.
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Your results
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How it works
Convert reported fuel economy between US mpg, Imperial mpg, kilometers per liter and liters per 100 kilometers. Consumption and economy are reciprocal quantities, so improving mpg decreases liters per 100 km rather than increasing it.
A few things to know
Strictly positive inputs only. Does not calculate actual economy from trip distance and fuel, predict driving conditions, compare test cycles, calculate fuel price, or convert electric-vehicle energy consumption. Input gallon definition must be known; display uses up to 12 significant digits.
When to use this tool
Fuel economy and fuel consumption express the same relationship in opposite directions. Higher miles per gallon or kilometers per liter means more distance per fuel amount, while lower liters per 100 kilometers means less fuel consumed over a fixed distance. This converter handles that reciprocal relationship and separates US liquid mpg from Imperial mpg. Enter a positive reported value and its exact unit. The tool translates the figure; it does not predict a vehicle’s real-world performance, fuel cost or comparability across test procedures.
- Read a US mpg figure in liters per 100 kilometers.
- Compare a stated Imperial mpg value with a metric consumption figure using the correct gallon.
- Translate a trip’s already calculated km/L economy into other reporting units without reversing its meaning.
How to use fuel economy converter
Enter positive economy or consumption
Use Value for the numeric reported quantity. Zero and negative inputs are rejected because their reciprocal conversion cannot represent a finite positive result.
Choose the exact source convention
Set From unit to L/100 km, km/L, mpg US or mpg Imperial. Gallon convention must come from the original source.
Read the target with its direction
Choose To unit and calculate. Review Converted fuel economy and the table, remembering that lower consumption and higher distance-per-fuel indicate less fuel use.
Thirty US mpg as liters per 100 km
Inputs
Value 30; From unit Miles per US liquid gallon (mpg US); To unit Liters per 100 km (L/100 km).
Result
Converted fuel economy is 7.84048611111 L/100 km. The table also gives approximately 12.7543112229 km/L and 36.0284977651 mpg Imperial.
What it means
The unit relationship uses the US liquid gallon and international mile. A source stating 30 Imperial mpg instead converts to about 9.41603121107 L/100 km, so the gallon label changes the comparison substantially.
Common mistakes to avoid
Treating larger L/100 km as better
Consumption is fuel per distance, so a smaller value means less fuel use. Economy in mpg or km/L runs in the opposite direction.
Substituting US and Imperial mpg
Their gallon volumes differ. A conversion needs the source convention, even when both readings are abbreviated mpg.
Comparing ratings from different procedures
Unit conversion does not make different test cycles, driving conditions or measurement methods equivalent.
Frequently asked questions
Definitions, edge cases, and practical next steps for this tool. Search all tool FAQs ↗
How are km/L and L/100 km related?
L/100 km equals 100 divided by km/L. The reverse uses the same reciprocal formula. A value of 20 km/L therefore equals 5 L/100 km. Multiplying by one fixed scale factor would not correctly convert this reciprocal pair.
How is US mpg converted to L/100 km?
Divide the constant 100 × 3.785411784 ÷ 1.609344 by US mpg. Those values represent liters per US liquid gallon and kilometers per international mile. The result uses the factors before display rounding rather than a heavily rounded conversion shortcut.
What changes for Imperial mpg?
The gallon factor becomes 4.54609 liters instead of the US liquid gallon’s 3.785411784 liters. For the same physical fuel economy, the numerical Imperial mpg is larger. An unlabeled mpg value cannot safely be converted without determining its gallon convention.
Why are zero and negative inputs rejected?
A zero distance-per-fuel value would require division by zero to express reciprocal consumption. A zero consumption value similarly cannot produce a finite economy value. Negative values do not represent the positive fuel-use quantities modeled by this converter.
Does a 10% mpg increase mean a 10% consumption reduction?
No. Reciprocal measures change by different percentages. For example, increasing economy from 20 to 22 km/L changes consumption from 5 to about 4.545 L/100 km, a reduction of about 9.09%. Convert the before and after values separately.
Can I calculate economy from distance and fuel used here?
The tool accepts a previously calculated economy or consumption figure, not separate trip inputs. Calculate distance divided by fuel for km/L, or fuel divided by distance times 100 for L/100 km, using compatible units before converting that result.
Can I average several mpg values before converting?
A simple average can be misleading when trips differ in distance or fuel use. Combine actual total distance and total fuel to calculate the aggregate economy, then convert it. This tool does not infer trip weights or aggregate several readings.
Does the result estimate fuel costs or electric-vehicle use?
No. Fuel price, trip length and energy-per-distance units are not inputs. The result only changes the reporting unit of a fuel economy quantity. It does not predict consumption under your route, speed, load, weather or charging conditions.
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Sources and method
Use the references below to check definitions and platform guidance. The model’s scope and limits are explained above. Read our editorial standards.