Everything You Need To Know About Miles Per Gallon (mpg)

Everything You Need To Know About Miles Per Gallon (mpg)
26 Mar 2019
By Ross Wild

We've all heard of the term miles per gallon and that the higher it is the better - but do you actully know what it means and what urban mpg, extra urban mpg and combined mpg means? In today's blog we explore the wonderful world of fuel consumption!

What is miles per gallon (MPG)?

When you are in the process of obtaining a new car, you will often hear a salesman mention 'miles per gallon' or 'fuel economy'. Put simply, all MPG does is tell you approximately how far your vehicle will travel based upon a single UK gallon, which equates to approximately 4.55 litres of fuel. A vehicle’s miles per gallon is always an estimate because of the sheer number of variables the vehicle and tests have to consider and a vehicle’s MPG score should be used as a guideline only.

What is the importance of MPG?

Your MPG figure is actually more important than you may think, as it is an indication into how much fuel you are using and how many miles out of that fuel your car is capable of doing. Put simply, the higher your miles per gallon reads the more you can drive between petrol pump visits. Also, miles per gallon is also a good indicator along with CO2 emissions to express how economical your car is. Extracting fossil fuels and processing them to make petrol and diesel is not good for the environment so a high miles per gallon rating and a low CO2 emission rating is a greener car overall and helps reduce your personal carbon footprint.

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Fuel Pumps

How are miles per gallon scores calculated? 

You may be wondering how can manufacturers figure out how many miles per gallon a car can do without actually running real-life tests. Well, to put it short they do it in a lab. A vehicle’s official fuel economy (AVG-MPG), which you will see on the car's specifications when purchasing or leasing a vehicle is calculated to an EU standard. Historically it was tested in a controlled and efficient laboratory testing program called the new European driving cycle or shortened to NEDC. The other program used to test fuel emissions and the procedure more commonly used to this day is shortened to WLTP (Worldwide Harmonised Light Vehicle Test); WLTP is based upon real-driving data and better matches on-road performance rather than NEDC which was theoretically based.  

Home Tip- If you were to try and calculate your own miles per gallon, you would have to wait until you were next filling up your car with fuel and take note of how much petrol or diesel you have filled your tank with and then divide by the distance in miles (on your odometer) by the amount of fuel you have filled up with. Some vehicles will actually tell you what your average miles per gallon are during your commute, but it can change dependant on your style of driving etc...

EC- Simply means European Commission

What is Urban mpg?

Put simply, when you see EC Urban MPG, it's supposed to represent the average miles per gallon for modern inner city driving. The Urban Cycle test consists of acceleration, deceleration, idling and steady speed testing with a maximum speed of 31 mph over a distance of 2.5 miles. It's carried out in a laboratory with a change in temperature between 20 and 30 degrees, with the car being tested from a cold start, which is representative of how the vehicle would manage city driving.

City Driving Image

Urban MPG can be very hard to predict due to the changeability and randomness that city driving has to offer. Some days traffic may be crazy, meaning that you are stop-starting constantly, and other days you may have a clear run, there is genuinely no say. That is why the Urban mpg cycle should be used more as a guideline for city drivers as opposed to an exact measure. The Urban EC figure is usually much lower than other ratings because city driving is very uneconomical for fossil fuel vehicles.

What is Extra Urban mpg?

EC Extra Urban is representative of country road driving (A-roads and B-roads) as well as occasional motorway driving and is usually tested straight after the Urban Cycle is complete. It mimics this style of driving through steady speed driving, accelerations, decelerations and some idling with a maximum speed of 75 mph and an average of 39 mph being tested over a distance of 4.3 miles with a warmed up engine.

Countryside Driving

What is Combined mpg?

Combined mpg relates to the average miles per gallon calculated between the Urban and Extra-Urban readings and is usually the statistic that most driver’s look for when contemplating a vehicle for its fuel economy. It could also be considered the most accurate reading for a variety of drivers and especially people who live outside of large cities because the combined reading incorporates the two readings so would make sense to people who commute from the countryside into the city for work and experience both urban and extra-urban styles of driving.

My Fuel Consumption is Drastically Different From 
the Real World, What Should I Do? 

Sometimes you may find that you are filling up at the petrol station more than you anticipated and having to reach deeper into your pocket as the month goes by. You might be looking at your car’s internal mpg measurement to find it is way off what the manufacturer said it was in the brochure or on a website such as ours who get their data from suppliers such as CAP. On rare occasions it may be because of incorrect data, flawed tests or it may come as a surprise that it actually may be a result of your own actions. You should review the route you take to work as you may be adding extra unnecessary miles on every day which in turn will add up at the end of the month or maybe consider looking for a vehicle with better fuel consumption.

On the point made that the data can actually be incorrect; manufacturers have actually been found to violate motoring laws with the most notorious being the Volkswagen emissions scandal, where VW had intentionally programmed turbocharged direct injection diesel engines to activate their emission controls during testing over a series of 6 years from 2009 to 2015. This meant that many vehicles statistics were obscured and inaccurate, resulting in fines and lawsuits for the VW Group - although this had nothing to do with mpg numbers it is nonetheless a cautionary tale that you shouldn't blindly believe every statistic about your car and to take care to research before committing to a purchase.

Although this is a thing of the past (we hope), drivers should never use mpg statistics as gospel and should be aware that mpg scores aren’t 100% accurate, but figures are always very close to the estimated figure.


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Ways to improve miles per gallon 

If you admit to being a petrolhead, unfortunately, this section may not be the best information for you. Manufacturers would assume that drivers are driving cautiously and reasonable when they state their potential mpg scores; if you don’t drive economically then don’t expect your car’s actual mpg to match that of the brochures. If you would like to save a bit of money and harm the environment less, it is of mass importance to try and conserve fuel as best as you can. You can do this through a few different methods, some of which including:

Quick Tips:

  • Keep your tires inflated and at the right pressure
  • Don't over-rev and floor the accelerator (drive sensible)
  • Use of cruise control
  • Use recommended fuel
  • Don't overload your car with unneeded things
  • Don't stress out your engine and use the correct gears
  • Servicing your vehicle

Electric Vehicles

It could be argued that electric vehicles are considered to be the future of the motoring industry due to their cheap running costs and zero fuel emissions, and they are becoming more popular than ever. Electric vehicles like the BMW i3 are particularly attractive to drivers who want to save on fuel costs. They are fuel efficient because of the use of an electric motor with a large battery pack which is then charged from being plugged in, instead of refuelling up with diesel or petrol. As there is no fuel being burned there are no emissions and because there’s no fuel there can’t be an estimate miles per GALLON. However, there will be miles per charge or a similar metric available.

Hydrogen Vehicles

A step beyond electric vehicles and a new prospect to the industry are well-developed hydrogen vehicles with the likes of the Toyota Mirai. The hydrogen is converted from chemical energy to mechanical energy through the reaction of hydrogen and oxygen in a fuel cell, which in-turn means that the only byproduct at point of use is actually only water. Once again, as no fuel is present there won’t be any emissions or miles per gallon metric.

Toyota Mirai

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