How to use this calculator
- Enter the requested journey or vehicle details.
- Select the matching units and options.
- Choose Calculate to see the estimate and supporting values.
- Change any value and calculate again to compare scenarios.
How the calculation works
The calculator normalises distance to kilometres and fuel to litres. UK and US MPG use different gallon sizes, so their results are not interchangeable.
Formula: UK MPG = miles ÷ Imperial gallons. L/100km = litres ÷ kilometres × 100. UK MPG to L/100km = 282.481 ÷ MPG.
Worked example
A vehicle travelling 400 miles using 40 litres returns about 45.46 UK MPG, 37.85 US MPG and 6.21 L/100km.
What can affect the result?
Fill-level accuracy, odometer accuracy, driving conditions and idling affect measured economy.
Frequently asked questions
Why is UK MPG higher than US MPG?
An Imperial gallon is larger than a US gallon.
Can I convert without entering a trip?
Yes. Choose conversion mode and enter one economy value.
