MPG Calculator

Fuel economy is an indicator whose importance varies from region to region. In the United States, fuel economy is usually expressed as miles per gallon, with a higher number indicating better vehicle efficiency. In most of the rest of the world it is expressed in liters per 100 kilometers, with a lower number being better.

This calculator supports both representations. You can enter two of the three values - distance traveled, fuel consumed and fuel efficiency - and it will calculate the missing value. With additional features enabled you can also calculate your trip cost, predict your annual driving conditions, estimate your CO2 emissions and compare your vehicle with others.

What can be calculated?

The focus is on three quantities: the distance traveled, the fuel consumed and the resulting fuel consumption. Since these three values are connected by a relationship, you can calculate the missing value if two of them are known.

If you leave the fuel consumption blank, it will calculate miles per gallon (MPG) for a single trip. If you enter the fuel consumption along with one of the other two values, then it can also calculate how much fuel is needed for a single trip or how far you can go on a full tank.

Calculation method

Fuel consumption is calculated by dividing the distance traveled by the fuel consumed.

If you travel 500 km and use 40 liters of fuel, your consumption is 12.5 km per liter or 8.0 L/100km which is approximately 29.4 US MPG. By rearranging the formula, you can also calculate how much fuel you need for a certain distance (distance divided by consumption) and how far you can go with a given amount of fuel (fuel multiplied by consumption).

MPG and L/100km have opposite trends.

Because miles per gallon and liters per 100 kilometers are inverse measurements, one measurement will increase while the other decreases. To convert between these two units, divide 235.215 by the corresponding value.

So, 30 US MPG is approximately equal to 7.84 L/100 km and 8 L/100 km is approximately equal to 29.4 US MPG. These two units are inversely proportional so this method of conversion can be used in both directions.

A U.S. gallon is not the same as a British gallon.

A U.S. gallon is 3.785 liters and a British gallon is 4.546 liters, so they are not directly interchangeable. For the same vehicle using the same fuel, it would calculate to about 30 U.S. MPG or about 36 UK MPG. The reference table in this calculator shows both standards side by side so that you can see the differences at a glance.

How to measure actual consumption:

To measure fuel consumption precisely, fill the tank to capacity and then note down the reading before refilling it again. Fill up completely, record your odometer or reset the trip meter to zero, drive as normal and refill the tank again. The amount of petrol needed for the second filling is what you have used and the distance travelled will be indicated by the reading on the odometer.

Before you consider this value reliable, you need to measure it over a long enough distance. Drive at least 100 km or 60 miles. Short distances, cold starts and stop-and-go traffic conditions give worse results than constant speed. So the data for a full tank in city driving is not comparable with that of a long highway drive.

Why the stated values may be optimistic:

The official EPA and WLTP ratings are from standardized lab test cycles, not your daily drive. Cold temperatures, short trips, hard acceleration, roof racks, under-inflated tires all reduce the stated numbers so most drivers will see values in practice that are about 80% to 90% of the stated value.