Gas Mileage Calculator (MPG & L/100km)

Quickly compute fuel economy from odometer readings or trip miles, plus fuel cost per mile/km and total trip cost.

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Choose how you want to enter distance.
Tip: For best accuracy, fill to the same level each time.
Fuel economy
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Alternate
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Trip distance
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Fuel used
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Cost per distance
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Total fuel cost
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How to calculate gas mileage

US units: MPG = miles / gallons. Example: 349.7 miles ÷ 12.7 gal = 27.53 MPG.

Metric units: L/100km = (liters × 100) / kilometers. Example: 55.5 L × 100 ÷ 563 km = 9.86 L/100km.

Conversion shortcuts: MPG = 235.215 / (L/100km) and L/100km = 235.215 / MPG.

Worked example

Odometer start 12,340.5 → end 12,690.2 gives distance 349.7 miles. Fuel added 12.7 gal; price $3.79/gal.

  • MPG = 349.7 ÷ 12.7 = 27.53 MPG
  • Cost per mile = $3.79 ÷ 27.53 = $0.138
  • Total cost = 12.7 × $3.79 = $48.13

FAQs

Is trip computer MPG accurate?

It’s usually close, but fill-to-fill calculations are more consistent over time.

Does AC or speed affect MPG?

Yes—higher speeds, aggressive acceleration, and AC/heating can all reduce fuel economy.