Fuel Consumption Converter
Convert between MPG (US), MPG (UK), L/100km, and km/L fuel efficiency units.
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How to use this calculator
- 1
Enter your fuel consumption value.
- 2
Select the unit you are converting from (e.g. MPG US).
- 3
Select the target unit (e.g. L/100km).
- 4
The result appears instantly. Note that higher MPG = lower L/100km (inverse relationship).
Frequently asked questions
How do I change L/100 km to mpg?
Divide 235.21458333 by the L/100 km figure for US mpg, or 282.48093633 for imperial mpg. These constants come from 100 × 3.785411784 ÷ 1.609344 and 100 × 4.54609 ÷ 1.609344. So 8 L/100 km is 29.40182292 US mpg or 35.31011704 imperial mpg.
Why are US and UK mpg different?
The gallons differ. A US gallon is 3.785411784 L and an imperial gallon is 4.54609 L, about 20 percent larger. The same car therefore reads a higher mpg in imperial units: 30 US mpg equals 36.02849777 imperial mpg, and 30 imperial mpg is 24.98022554 US mpg.
Is a bigger or smaller number better?
For km/L and mpg, higher is better because they measure distance per fuel. For L/100 km, lower is better because it measures fuel per distance. So 6 L/100 km (39.20243055 US mpg) beats 10 L/100 km (23.52145833 US mpg).
Why does 0 give a dash for some conversions?
A reading of 0 mpg would mean infinite fuel per 100 km, and 0 L/100 km would mean infinite mpg. Both are undefined as a finite number, so the tool shows a dash instead of a misleading zero.
Can I average mpg figures from several trips?
Not by adding them up and dividing. mpg is distance divided by fuel, so combine totals: total distance over total fuel. Converting each trip to L/100 km first makes the plain average valid for equal distances.
What is km/L?
Kilometres per litre is distance per fuel, the metric counterpart of mpg: 12.5 km/L is exactly 8 L/100 km, and 15 km/L is 6.666666667 L/100 km. The tool lists it with L/100 km, which is the form used on much of Europe’s and Canada’s labels.
Does it cover electric vehicles?
No. The units here are litres or gallons of fuel for a distance. Electric consumption in kWh per 100 km, or MPGe, is a different measure and is not included. Hybrid cars that burn fuel can be converted by their fuel figure.
Fuel economy units: L/100 km, km/L, US mpg and imperial mpg
Fuel per distance versus distance per fuel
Fuel economy can be stated two ways. L/100 km gives litres of fuel burned over 100 km, so a smaller number means a more efficient car. Kilometres per litre and miles per gallon give distance per fuel, so a larger number is better. The converter moves between them by dividing a constant by the value: 235.21458333 for US mpg and 282.48093633 for imperial mpg, derived from 3.785411784 L, 4.54609 L and 1.609344 km. The same relationship explains the exact equality 100 km/L = 1 L/100 km, so km/L and L/100 km are reciprocals scaled by 100.
Reference values taken from the converter
Each row starts from a L/100 km figure and shows the same efficiency in the other three units, copied from the tool’s output.
| L/100 km | km/L | US mpg | Imperial mpg |
|---|---|---|---|
| 5 | 20 | 47.04291667 | 56.49618727 |
| 6 | 16.66666667 | 39.20243055 | 47.08015606 |
| 7 | 14.28571429 | 33.60208333 | 40.35441948 |
| 8 | 12.5 | 29.40182292 | 35.31011704 |
| 9 | 11.11111111 | 26.1349537 | 31.3867707 |
| 10 | 10 | 23.52145833 | 28.24809363 |
Worked examples: both gallons
A car rated 30 US mpg uses 7.840486111 L/100 km, equal to 12.75431122 km/L or 36.02849777 imperial mpg. A car rated 30 imperial mpg uses 9.416031211 L/100 km and is only 24.98022554 US mpg. At 15 km/L, consumption is 6.666666667 L/100 km, or 35.2821875 US mpg. Always state which gallon you mean.
Why mpg gains look uneven
Because mpg is the inverse of consumption, equal mpg steps are not equal fuel savings. Going from 20 to 25 US mpg lowers consumption from 11.76072917 to 9.408583333 L/100 km, a saving of about 2.352 L per 100 km. A larger rise from 40 to 50 US mpg, 5.880364583 to 4.704291667 L/100 km, saves only about 1.176. L/100 km makes such comparisons honest.
Edge cases and scope
A zero input yields a dash because the inverse is infinite. The tool handles fuel for a distance only; electric cars, trip costs and tank range are separate calculations. Results show up to ten significant digits, which is more than any trip computer measures. Remember too that consumption depends on speed, load and conditions, so a converted rating is a label comparison and not a prediction of your own result.
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Results are estimates for informational purposes only and do not constitute professional financial, medical, legal, or technical advice. Read full disclaimer →