Result
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Facts and limits of this method
| Relationship type | Inverse (nonlinear) — a lower L/100km means a higher mpg |
|---|---|
| 1 US gallon | 3.785411784 liters |
| 1 UK (imperial) gallon | 4.54609 liters — noticeably larger than the US gallon |
| km/L → mpg US factor | × 2.352145833 |
| km/L → mpg UK factor | × 2.824809363 |
When it misleads you
- L/100km and mpg aren't related by simple multiplication but by an inverse relationship through the intermediate "kilometers per liter" unit — as L/100km decreases (a more efficient car), mpg increases, not decreases.
- The US gallon (3.785411784 L) and the UK imperial gallon (4.54609 L) are different units, differing by almost 20%; 30 mpg US and 30 mpg UK represent noticeably different real fuel consumption — don't mix them up when reading foreign car reviews.
- The converter performs a purely arithmetic unit conversion — it doesn't account for differences in measurement methodology (such as the European WLTP cycle versus the US EPA cycle), which also affects the final figures in car specifications.
- Entering 0 as consumption in L/100km makes the mpg result formally approach infinity (the car uses no fuel) — the converter doesn't show a numeric result in that case.
How it is calculated
The entered value is first converted to kilometers per liter (km/L) — for example, from L/100km using km/L = 100 / (L/100km), from mpg by dividing by the corresponding US or UK gallon factor.
If the "from" unit is already km/L, this step leaves the number unchanged.
The km/L value is then converted to the target unit using the inverse formula.
The result is rounded to the chosen number of decimal places and updates instantly whenever the value, units or precision change.
Questions and answers
Why does a lower L/100km give a higher mpg?
Because they measure the same thing differently: L/100km shows consumption per distance (lower is more efficient), while mpg shows distance per volume of fuel (higher is more efficient) — the relationship between them is inverse.
What's the difference between mpg US and mpg UK?
Just the gallon's volume: the US gallon (3.785 L) is smaller than the UK imperial gallon (4.546 L), so the same real fuel consumption converts to a number about 20% higher in mpg UK than in mpg US.
Does the converter account for the difference between European and US test cycles?
No, this is a purely arithmetic unit conversion — methodological differences between test cycles (WLTP, EPA, etc.) aren't accounted for.
Is my data sent anywhere?
No, the whole calculation runs in your browser.