FuelTripCost.

Driving cost tool

Fuel Economy Calculator

Measure economy from distance and fuel consumed over the same interval, then view four equivalent ways to express that consumption.

For converting odometer, pump, vehicle-listing, or travel records between US, UK, and metric units.

Measure your fuel economy

Enter distance driven and fuel used over the same interval. The result shows US MPG, Imperial MPG, L/100 km, and km/L.

For a fill-up measurement, start and finish with a full tank and use the fuel added at the second fill-up.

How to use this calculator

  1. Enter distance and choose miles or kilometres.
  2. Enter fuel used and choose US gallons, Imperial gallons, or litres.
  3. Calculate all four economy measures.
  4. Use the unit understood by the next calculator or comparison.

Formula and variables

  • US MPG = miles ÷ US gallons
  • Imperial MPG = miles ÷ Imperial gallons
  • L/100 km = litres ÷ kilometres × 100
  • km/L = kilometres ÷ litres

What each input means

  • 1 mile = exactly 1.609344 km.
  • 1 US gallon = 3.785411784 litres; 1 Imperial gallon = 4.54609 litres.

Choosing the right units

Imperial and US MPG differ because the gallon sizes differ. Higher MPG and km/L are better; lower L/100 km is better.

Worked examples

US fill-up

300 miles using 10 US gallons is 30 US MPG, 36.03 Imperial MPG, 7.84 L/100 km, and 12.75 km/L.

Metric interval

200 km using 16 litres is 8 L/100 km, 12.5 km/L, 29.40 US MPG, and 35.31 Imperial MPG.

Reading the result

Moving from 8 to 7 L/100 km or from 30 to 35 MPG both indicates better economy.

Real-world factors

  • Conversion preserves the same physical consumption.
  • Compare measurements from similar routes, loads, weather, and driving styles.

When to use it

  • Convert economy between regions.
  • Compare a fill-up with a metric specification.
  • Prepare an input for a trip-cost estimate.

Common mistakes

  • Treating US and Imperial MPG as identical.
  • Assuming higher L/100 km is better.
  • Mixing distance and fuel from different intervals.

Limits of the estimate

Does not provide official ratings, predict a trip, estimate fuel price, or remove measurement error.

Questions about this calculator

Are US MPG and Imperial MPG interchangeable?

No. The larger Imperial gallon produces a higher MPG number for the same consumption.

Which unit is best?

Use the unit your source and audience understand, and compare values only after converting them to the same unit.

Can this estimate trip cost?

Use its economy result in Fuel Cost Calculator with a distance and matching price unit.

Related calculators and guides

Gas Mileage CalculatorFuel Cost CalculatorCost Per Mile CalculatorCalculation methodology