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Gas Mileage Calculator

Measure real fuel economy from your odometer and fill-ups.

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Measure your real economy

Fill the tank, reset the trip meter, drive normally, then fill completely again and enter both figures.

Distance since last fill
Fuel used to refill
—L / 100 km
—km per litre
—MPG (US)
—MPG (imperial)

Compare two vehicles

Fuel economy

—

Quick conversion

MPG (US)L/100 kmkm/L

Real-world economy is routinely 10–20% worse than the official rating. Short trips, cold starts, high speeds, roof boxes and under-inflated tyres all cost fuel.

Quick Tool Overview

The Gas Mileage Calculator measures what your vehicle actually achieves rather than what the brochure claims, from the distance covered since your last fill and the fuel it took to refill. Results come in every common unit, and two vehicles can be compared side by side.

What it does
Calculates real-world fuel economy from odometer and fill-up figures
You give it
Distance driven and fuel used to refill
You get back
Your economy in MPG, km/L and L/100km, plus a comparison
Best for
Tracking a car's economy and comparing two vehicles
Calculators Free, unlimited use No sign-up Runs in your browser

About the Gas Mileage Calculator

Work out what your vehicle actually achieves rather than what the brochure claims. Enter the distance covered since your last fill and the amount of fuel it took to refill, and the calculator returns your real economy in every common unit.

The method that gives a reliable figure is tank to tank: fill completely, reset the trip meter, drive normally, then fill completely again and record the distance and the volume. Real-world economy is routinely 10 to 20 percent worse than the official rating, and it varies with speed, load, tyre pressure and how much of the drive is stop-start. A comparison panel puts two vehicles side by side and shows the annual fuel cost difference between them.

Key features of the Gas Mileage Calculator

The tank-to-tank method

Fill completely, reset the trip meter, drive normally, fill completely again — the only method that gives a reliable figure.

Every common unit

MPG (US and imperial), kilometres per litre and litres per 100 km from one measurement.

Realistic expectations

Real-world economy is routinely 10 to 20 percent worse than the official rating, and the page says so.

Two-vehicle comparison

Put two cars side by side and see the annual fuel cost difference between them.

What moves the number

Speed, load, tyre pressure and stop-start driving all change economy, which is why a measured figure beats a quoted one.

How to use the Gas Mileage Calculator

  1. 1

    Fill the tank completely

    Reset your trip meter, or note the odometer reading.

  2. 2

    Drive, then fill up again

    Fill completely once more and note the distance covered and the volume of fuel it took.

  3. 3

    Enter both figures

    Your economy is calculated in MPG, kilometres per litre and litres per 100 kilometres at once.

  4. 4

    Compare two vehicles

    Enter a second economy figure and an annual distance to see the running cost difference.

Frequently asked questions

Divide the miles driven by the gallons used to refill. 300 miles on 10 gallons is 30 miles per gallon. Do it over a full tank rather than a partial fill for a reliable number.

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