What is MPG?

When you’re shopping around for your next car, one of the most important things to consider is MPG – how many miles to the gallon it can do.

Here’s a look at how a car’s MPG is calculated and what you can do to improve overall fuel-efficiency.

When you’re shopping around for your next car, one of the most important things to consider is MPG – how many miles to the gallon it can do.

Here’s a look at how a car’s MPG is calculated and what you can do to improve overall fuel-efficiency.

Daniel Hutson
From the Motor team
4
minute read
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Posted 29 APRIL 2021

What does MPG mean?

MPG stands for miles per gallon – in other words, how many miles your car can travel on just one gallon of fuel in the tank.

So, theoretically, if your car has an MPG of 60, you should be able to drive for 60 miles before you run out of fuel.

MPG is used to measure the fuel-efficiency of a vehicle. The more miles per gallon your car does, the less you’ll spend on fuel. So, in an ideal world, a good MPG rating means you should have lower running costs, and you’ll also pay less in road tax.

It’s important to note that official MPG figures are calculated in a test lab using ‘ideal scenarios’ – they’re only an estimate and don’t always reflect real-world driving. However, they can give you a good idea of fuel economy when comparing different cars

What affects MPG?

The MPG of a car depends on a number of things, including:

When it comes to MPG and fuel-economy, a lot can also depend on the way you drive your car. For example, if you have a large, diesel-engine car, and you’re only driving a few miles each day around town, your fuel-economy won’t be as efficient as it would be if you were driving long journeys on the motorway.

Your MPG can also be compromised by weight. If you overload your car, the extra baggage can significantly lower how many miles per gallon you’ll be able to do. Even fitting optional larger wheels can have an impact, as the extra weight can cause more friction and a greater drag when you drive.

How is MPG calculated?

Official MPG figures – those you see in new car brochures – are calculated using the World harmonised Light-duty Vehicle Test (WLTP). It’s a bit of a mouthful, but not that complicated to understand.

The new WLTP test essentially involves a range of scenarios which give a clearer idea of how a car performs in real-world conditions: on main roads, in cities and towns, on rural roads and on long stretches of motorway. These results are combined to get an all-round MPG figure. Introduced in 2017, this new way of measuring a vehicle’s fuel economy is more accurate than the old NEDC test.

Official MPG vs True MPG?

In nearly all cases, the true MPG of a car is likely to be lower than ‘official figures’ – even for the most efficient vehicles. Although WLTP tests take into consideration different scenarios, they’re still carried out under laboratory conditions; the engine isn’t worked as hard as it would be in real life, so the resulting figures are only a rough estimation of what you’ll realistically be able to achieve.

Official figures also show what can typically be expected from a car that’s driven sensibly and within national speed limits.

How can I work out my car’s MPG?

As we’ve said, there are a lot of variables that go into estimating a car’s MPG – for example, it can depend on weather conditions, the type of road you’re driving on and the size of your car’s engine – the more powerful the car, the lower the MPG tends to be.

But a really simple way of working out how much fuel you’re consuming is to use your car’s odometer (the dial or display on your dashboard that tells you how many miles you’ve done).

The next time you fill up an empty (or almost empty) tank, set the odometer to zero. Then make a note of how many miles you can do on a full tank.

What is a good MPG?

In general, a good MPG should be anywhere between 50-60MPG. Anything in this range is likely to have lower running costs, and you should also pay less road tax. You might also find that some cars with a higher MPG are also cheaper to insure.

Having said that, one of the most fuel-efficient cars around at the moment is the Peugeot 208 1.5, which claims an impressive 76.3mpg.

At the other end of the scale, if you’ve got the funds to fork out for a Bugatti Chiron, you’ll only get a measly 11mpg. That’s right… the more prestigious the mark – Bugatti, Lamborghini, Ferrari, for example – the higher the running costs will be. But, let’s face it, if you can afford one of those beauties, MPG and fuel economy will hardly be a priority.

What does l/100km mean?

While here in the UK we still use miles per gallon, many other countries measure fuel efficiency in litres per 100km – how many litres of fuel a car will use after it’s driven 100km.

Basically, 1litre per 100km is the same as 282.5mpg. So, if you need to convert it into MPG, just divide the l/100km for your car by 282.5. Simply put, the higher the MPG and the lower the l/100km, the more fuel-efficient a car will be.

How do I convert MPG into MPL?

For many, the concept of still measuring a car’s efficiency in gallons seems ridiculous, not least because when we buy petrol and diesel in the UK, it’s in litres.

So, if you want to work out how far you’ve driven and how much fuel you’ve used, you’re going to have to convert.

Luckily, it’s a pretty simple calculation: if you want to know your car’s ‘miles per litre’, take its MPG figure and divide it by 4.54.

Will my car’s MPG change as it gets older?

Over time, your car won’t be as fuel-efficient as it once was, but regular servicing and good maintenance will help it stay as fuel efficient as possible.

However, a fuel-efficient car 10 years ago isn’t the same as a fuel-efficient car today. If you’re looking to buy a second-hand car, try not to go for something that’s more than a few years old. As a ballpark figure, try to aim for a car with an MPG around 40.

How can I improve my car’s MPG?

If you want to spend less time at the pumps, there are things you can do to improve the fuel efficiency of your car. Follow these tips to get more out of your tank of fuel:

  • Take care of your tyres – keep an eye on your tyre pressure. The wrong pressure means you’ll consume more fuel. Check the correct pressure in your vehicle handbook. Your tyres should be checked at least once a month, and additionally if you’re transporting a heavier load than usual, or before going on a long journey.
  • Get rid of clutter – clean out the boot and get rid of any unnecessary weight. The heavier your car is, the more fuel it will consume.
  • Change the way you drive – common habits like revving, braking hard and excessive, quick accelerating can mean you’re using more fuel than necessary.
  • Slow down! – cruising on the motorway at 60mph rather than 70mph can cut your fuel consumption by around 10%.
  • Don’t idle – if your car isn’t equipped with a stop/start function, cut the engine when you’re stuck in traffic for more than a minute or so.

Above all, keep your car regularly serviced and well-maintained. Not only will this help with fuel consumption, but it also means you’re less likely to break down.

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