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MPG Calculator

Calculate fuel efficiency (MPG) from odometer readings.

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Inputs

mi
mi
gal

Your values stay on this device.

Results

MPG
Cost per Mile$0.13
Distance Traveled350

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Assumptions

  • The tank is filled to the same level at the start and end of the measurement.
  • Odometer readings belong to the same trip window.
  • Gallons used and distance traveled are both positive values.

Sensitivity preview

Start Odometer -10%: MPG 108

Start Odometer Current: MPG 28

End Odometer Current: MPG 28

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About this Gas Mileage (MPG)

Monitoring your gas mileage is the best way to track your vehicle's health and your driving habits. A sudden drop in MPG can indicate engine trouble or under-inflated tires. This tool helps you calculate your exact MPG between fill-ups.

Who this calculator is for

  • Drivers who track fuel efficiency tank by tank.
  • Commuters and road-trippers watching the cost of every mile.
  • Anyone who wants to spot a sudden drop in fuel economy early.

When to use it

  • Calculate MPG after a fill-up.
  • Compare fuel economy across vehicles, routes, or seasons.
  • Estimate cost per mile for commuting or travel planning.

How to use this calculator

  1. Fill your tank completely and record the Start Odometer (or reset the trip counter).
  2. Drive until you need gas again.
  3. Fill the tank completely again. Record the Gallons pumped.
  4. Record the End Odometer.
  5. The result is your average MPG for that tank.

Key assumptions

  • The tank is filled to the same level at the start and end of the measurement.
  • Odometer readings belong to the same trip window.
  • Gallons used and distance traveled are both positive values.

Accuracy and testing

Review formula sources, default test cases, assumptions, unit handling, rounding rules, and changelog for this calculator.

View accuracy page

How this calculator works

1. Distance = End Odometer - Start Odometer. 2. MPG = Distance / Gallons Used. 3. Cost per Mile = (Gallons × Price) / Distance.

Inputs explained

Odometer Readings

The total mileage on your car. Alternatively, enter '0' for Start and the Trip mileage for End.

Gallons

The amount of fuel required to fill the tank back up to full.

Understanding your results

A higher MPG means better efficiency. Cost per Mile helps you budget for commuting or road trips.

Example scenarios

Commuter

Drove 300 miles. Pumped 10 gallons. MPG = 30.

Truck

Drove 300 miles. Pumped 20 gallons. MPG = 15.

Key Features

  • Odometer Logic
  • Cost Calculation
  • Efficiency Check

Tips & Best Practices

  • Use cruise control on highways to improve MPG.
  • Check tire pressure monthly; low pressure increases drag.
  • Don't 'top off' the tank after the nozzle clicks; it can damage the evaporative system and skews calculations.

Glossary of Terms

MPG
Miles Per Gallon. The standard unit of fuel efficiency in the US and UK.
Trip Odometer
A secondary odometer that can be reset to zero to track specific distances.

Frequently Asked Questions

Why does my MPG vary?
City driving (stop-and-go) consumes more fuel than highway driving. Winter blends of gas, AC usage, and heavy loads also reduce MPG.
How do I calculate L/100km?
L/100km is the inverse of MPG. To convert MPG to L/100km: 235.21 / MPG.
Do I need to fill the tank completely?
Yes. To accurately measure gallons used, you must fill the tank to the same level (full) at the start and end of the measurement period.