Measure, convert and compare

MPG and Fuel Economy Calculator

Calculate fuel economy, convert between US MPG and liters per 100 kilometers, and compare fuel costs over the same distance.

Fuel economy inputs

Fuel used must correspond to the measured distance, such as fuel added between consistent full-tank fill-ups. US gallons are used, not Imperial gallons. Unit switching converts populated inputs; all costs remain in USD. MPG improves when the number rises; L/100 km improves when the number falls.

Planned distance and fuel price estimate a future trip using this economy. Set price to 0 for an economy-only calculation. Both vehicles use the same trip distance and fuel price. Prices and MPG are your inputs, not live data or guaranteed performance.

Inputs stay in your browser.

Formulas and conversions

US MPG = miles / US gallons. Measured distance from an odometer = ending reading - starting reading. Metric consumption = liters / kilometers × 100. One mile is exactly 1.609344 km and one US liquid gallon is exactly 3.785411784 liters.

L/100 km = (100 × 3.785411784 / 1.609344) / US MPG. Fuel cost uses unrounded efficiency and fuel quantity, rounded to cents only at the end. The comparison subtracts the two rounded trip costs. Unit switching retains approximately 12 significant digits; tiny display differences may occur on repeated switches.

For several fill-ups, divide total distance by total fuel rather than averaging individual MPG readings. Traffic, terrain, weather and load affect future fuel economy.

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