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Fuel Economy Converter Calculator

Work out fuel economy converter instantly with clear inputs, formula shown and shareable results.

About Fuel Economy Converter Calculator

Fuel economy comes in two opposite flavours. Miles per gallon and km/L are 'distance per fuel' — higher is better. Litres per 100 km is 'fuel per distance' — lower is better. Because they are reciprocals, you cannot convert with a single multiplier: the calculator normalises the input to L/100 km first, then derives the rest. This also explains why saving fuel going from 15 to 20 mpg is a far bigger gain than going from 40 to 45 mpg, even though both are a 5 mpg step.

Formulas

mpg (US) → L/100 km

L/100 km = 235.214583 ÷ mpg(US)

mpg (UK) → L/100 km

L/100 km = 282.480936 ÷ mpg(UK)

km/L → L/100 km

L/100 km = 100 ÷ (km/L)

Worked example

With the default values below, Fuel Economy Converter Calculator returns Litres per 100 km of 7.840. Change any input above and every figure here is recalculated in your browser.

Inputs used

Fuel economy figureminimum 0.1
30
Given asone of Miles per US gallon (mpg US), Miles per Imperial gallon (mpg UK), Litres per 100 km (L/100 km), Kilometres per litre (km/L)
Miles per US gallon (mpg US)

Results

Litres per 100 km
7.840
Miles per US Gallon
30.000
Miles per Imperial Gallon
36.028
Kilometres per Litre
12.754

Step by step

  1. 1Values used
  2. 2mpg (US) → L/100 km
  3. 3mpg (UK) → L/100 km
  4. 4km/L → L/100 km
  5. 5Litres per 100 km= 7.840
  6. 6Miles per US Gallon= 30.000
  7. 7Miles per Imperial Gallon= 36.028
  8. 8Kilometres per Litre= 12.754

Assumptions and limits

  • The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why are US and Imperial mpg different?

The gallons differ. A US gallon is 3.785 L and an Imperial gallon is 4.546 L, so the same car scores about 20% more mpg on the UK scale than the US one.

Why is L/100 km considered a better measure?

Because fuel cost scales linearly with it. Halving L/100 km halves your fuel spend, whereas an extra 5 mpg means very different savings depending on where you started.

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