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Measured MPG, Fuel Consumption & Trip Cost

Calculate economy from trip distance and fuel used, distinguish US from UK MPG, and apply an entered fuel price.

  • Formula & worked example
  • Private in your browser
  • No signup
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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

Private by default

Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

Travelling 100 miles on two UK gallons gives 50 UK MPG. Those two gallons equal 9.09218 litres, costing 18.18436 at 2 per litre.

MPG = miles ÷ gallons; litres per 100 km = litres × 100 ÷ kilometres; cost = volume × entered unit price

Worked example

Enter these known values and leave the other values blank.

Measured distance
100 mi
Measured fuel volume
9.09218 L
Entered price per fuel unit
2 USD / L
Measured economy or consumption
50 UK mpg
Fuel cost
18.18 USD

Assumptions and limitations

  • Distance, fuel volume and economy are positive. Entered price and cost can be zero.
  • Fuel economy is an average over the measured trip, not a forecast of every future driving condition.
  • The example uses UK MPG and litres. The retained unit selectors also support US MPG and other consumption units.
  • Currency selection does not retrieve prices or exchange rates.

Common questions

Why are US and UK MPG different?

A UK gallon is 4.54609 litres; a US gallon is 3.785411784 litres. The same fuel efficiency therefore has different MPG values.

Can I calculate fuel from a known MPG?

Yes. Enter distance and the economy value with the correct gallon selector to calculate fuel volume.

References

Bookify includes zero-priced fuel while retaining positive measured distance and fuel volume. Bookify replaces the captured rounded US gallon with the exact 3.785411784-liter definition. US MPG uses the same exact US gallon as volume and price inputs.

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