Fuel economy is a decisive factor for many motorists while buying a new car and getting a decent mpg figure is a way of measuring this factor. We explain in this guide how mpg figures work, the different kinds and how such things are measured.
So what does MPG stand for? Well it stands for miles per gallon and indicates how fuel efficient a car is.
In a nutshell, the higher a vehicles MPG figure, the higher the fuel economy and therefore the longer it will travel on a single gallon of petrol – hence the acronym MPG (Miles Per Gallon).
So, for example, take something like a Ford Fiesta 123bhp 1.0-litre EcoBoost petrol – a very popular supermini. This has a 42 litre fuel tank and claims to offer an average of 66mpg. As 42 litres equates to around nine gallons, Ford expects that you will be able to travel 66 miles for every gallon of petrol you put in the fuel tank – effectively meaning that on average you can potentially travel up to 594 miles with a single tank of fuel.
Each new car in Britain has three official fuel consumption ratings: Urban, Extra Urban and Combined.
What is Urban MPG?
Urban MPG measures how efficient a car is when driving in a city or town. The Urban figure will usually be lower than other types of MPG figure, due to the constant fluctuation in driving style – stopping and starting for example.
What is Extra Urban MPG?
Extra Urban MPG is an assessment of how efficient a car is when driven on the roads surrounding cities or towns.
What is Combined MPG?
Combined MPG is the average fuel economy figure a manufacturer comes up with for a car when its figures for urban and extra urban MPG are combined.
When it comes to buying a car, combined MPG is the figure that most will focus on since it represents an average of what you can achieve. Most websites that review cars, including here at Car Keys, will use the combined MPG figure when discussing how efficient a model is.
How can I work out my car's MPG?
An effective way of calculating your car’s real-life MPG is to first fill up the vehicle’s fuel tank until the fuel pump cuts off. Next, reset the trip meter reading on the dashboard so you can record how many miles you do before the next time you fill up. When this is done, drive normally until you next have to fill up.
Fill up the fuel tank again and make note of how many litres of fuel you put in. When the tank is refilled, make note of the reading on the trip meter before you reset it again. You should be left with two numbers – the number of miles since you previously filled up and the number of litres you have just put in the car’s fuel tank.
Using the following formula, you should be able to calculate your car’s mpg: number of miles divided by the litres of fuel multiplied by 4.54.
How is a car's MPG tested?
Instead of using an actual road, manufactures will put their cars to the test in a laboratory on a rolling road. Every car will undergo the same series of standard tests which will ultimately result in three different figures.
What figure is considered good for MPG?
Whether or not a fuel economy figure for a car can be considered good depends on a lot of variables. These variables include the type of vehicle you’re looking at, its engine size, what fuel it uses and your own expectations.
As a general rule of thumb, an average-sized car can probably be considered good for fuel economy if it’s petrol-run and returns 50mpg combined or more, or it’s diesel-run and returns 60mpg combined or more.
For a sports car or any sort of performance model, a fuel economy of 40mpg or better can be considered a decent return.