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Gas Mileage Calculator

Work out your car’s real gas mileage in MPG and liters per 100 km.

Results

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For the best result, fill the tank, reset your trip meter, drive normally, then fill the tank again. Use the miles and gallons from the second fill. US gallons are used.

Quick Answer

Gas mileage is miles driven divided by gallons used. If you drive 320 miles on 12 gallons, your car gets 26.67 MPG, which is 8.82 liters per 100 km.

Last updated: 2 November 2026 · How we calculate this: miles divided by gallons

Table of Contents

How This Gas Mileage Calculator Works

Your dashboard reading is only an estimate. This calculator uses the miles you drove and the gallons you added at the pump, so it shows your real fuel economy.

Quick explanation: MPG = miles ÷ gallons.

  • Miles: distance since your last full tank.
  • Gallons: the amount shown at the pump when you refill.
  • Price: optional, to show your cost per mile.

Core Formulas

  • MPG: miles ÷ gallons
  • L/100 km: 235.214583 ÷ MPG
  • km/L: MPG × 0.425144
  • Cost per mile: price per gallon ÷ MPG

Worked Example

You drive 410 miles, then refill with 13.5 gallons.

  • MPG = 410 ÷ 13.5 = 30.37
  • L/100 km = 235.21 ÷ 30.37 = 7.74

Why Your MPG Changes

  • Driving style: hard braking and fast starts use more fuel.
  • Trip length: short trips are often less efficient.
  • Weather: cold weather can lower fuel economy.
  • Upkeep: tire pressure and regular service both matter.

Frequently Asked Questions

Divide the miles you drove by the gallons you used. 300 miles on 10 gallons is 30 MPG.

Divide 235.21 by your MPG. 30 MPG is about 7.84 L/100 km.

It depends on the vehicle type. Compare your result with the official figure for your car at FuelEconomy.gov.

Speed, traffic, load, weather and short trips can all lower it.

It is an estimate. The fill-up method on this page is a useful way to check it.

References & Sources

SourceUsed ForLink
U.S. Department of Energy, FuelEconomy.gov Fuel economy information. https://www.fueleconomy.gov/
Wikipedia, Fuel economy in automobiles MPG to L/100 km conversion. https://en.wikipedia.org/wiki/Fuel_economy_in_automobiles