What is MPG?

What does MPG mean?

MPG is a measure of a vehicle's fuel economy (also known as "fuel consumption"). This means miles per gallon. MPG numbers tell you how many miles a car can go on a gallon of fuel.

A car listed as getting 45.6mpg can go 45.6mpg of fuel. A car that can go 99.9 miles per gallon can go 99.9 miles per gallon of fuel. It really is that simple.

At Cazoo, we use the "official" MPG averages published by the vehicle manufacturer. Other sources of information may use different numbers after conducting their own tests.

How is MPG measured?

The procedures for measuring a car's fuel consumption have changed many times over the years. The current procedure is called WLTP - Worldwide Harmonized Passenger Car Test Procedure. All vehicles sold in the UK after 1 September 2019 have passed this fuel economy test. (The previous testing procedure was different - we will return to it a little later.)  

WLTP is conducted in a lab, but it is designed to reflect real driving. Cars "ride" on a rolling road - essentially a treadmill for cars. Each car is controlled in exactly the same way through a series of accelerations, decelerations and movement at different speeds. Sounds simple enough, but it's actually incredibly complex.

The tests are designed to simulate driving on all types of roads, including city streets and motorways. The amount of fuel used is measured and a fairly simple calculation shows the vehicle's MPG.

What is the difference between NEDC and WLTP?

The previous fuel economy test used in Europe was called the New European Driving Cycle (NEDC). Although it was a level playing field since all cars passed the same test, most car owners found their cars far from "official" MPG.

The WLTP numbers are lower (and more realistic). This is why some old cars seem to be more economical than more modern ones. The car hasn't changed, but the test has.

This is a potentially confusing situation and it can be difficult to figure out if your vehicle's MPG readings were produced by NEDC or WLTP. If your vehicle was manufactured after 2017, it was subject to the WLTP. All vehicles sold after September 1, 2019 were subject to the WLTP.

Why are there several different MPG figures for each vehicle?

Car manufacturers release several different MPG values ​​for their vehicles. These numbers are commonly referred to as urban MPG, suburban MPG and combined MPG and refer to different driving situations. 

The urban MPG tells you how much fuel the car will use on a city trip, while the extra-urban MPG tells you how much fuel the car will use on a trip that includes light city driving and high-speed A roads.

The combined MPG is average. It tells you how much fuel the car will use on a trip that includes all types of roads - cities, villages, highways. At Cazoo, we assign values ​​for combined fuel consumption per gallon because that is the closest relationship to the way most people drive.

How accurate are the official MPG numbers?

All official MPG figures should be taken as a guideline only. The fuel economy you get from your car depends on how you drive. As such, you can never get close to or beat the official MPG figures. In general, the combined WLTP should be fairly close to what you would get if your driving habits and style are average. 

However, there are caveats. Official MPG figures for plug-in hybrid vehicles are often very optimistic. You can see official MPG numbers for these cars running in the hundreds, but you're unlikely to come close to that in the real world. The discrepancy is due to the fact that real world fuel economy depends entirely on whether you keep your battery fully charged and how you drive.

How to calculate my car's MPG?

Each vehicle has an on-board computer that displays current and long-term MPG. You can reset the trip computer if you want to record a new set of numbers.

The trip computer is a good guide, but it is not always 100% accurate. If you want to know exactly how many miles per gallon your car is consuming, you need to calculate it yourself. Fortunately, this is not difficult to do.

Fill your vehicle's fuel tank until the pump turns off. Record the mileage displayed on the odometer and/or reset the mileage to zero on the trip computer.

The next time you fill up your car's fuel tank (again, until the pump clicks), pay attention to the amount of fuel filled. This will be in liters, so divide by 4.546 to get the number of gallons. Pay attention to the mileage on the odometer or the mileage reading on the trip computer. Divide those miles into gallons and you have your car's MPG.

Consider this example:

52.8 liters ÷ 4.546 = 11.615 gallons

368 miles ÷ 11.615 gallons = 31.683 mpg

What does l/100km mean?

L/100 km is another unit of measure for a car's fuel consumption. This means liters per 100 kilometers. It is used throughout Europe and in other countries in the metric system. Sometimes the unit km/l is also used - kilometers per liter. You can calculate MPG from l/100km by simply dividing 282.5 by the number of l/100km.

Can I improve my car's MPG?

The best place to start is to make sure your car is as aerodynamic as possible. For example, open windows and roof racks block the flow of air around the vehicle. The engine has to work a little harder to push the car forward, which worsens fuel economy.

It is also vital to inflate tires to the correct pressure. A low-pressure tire bulges, creating a larger "contact patch" with the road. This creates more friction than usual and the engine has to work harder to overcome it, which worsens fuel economy.

It is worth noting that the more wheels a car has, the worse its fuel efficiency will be. A high-spec car with 20-inch wheels may look great, but its fuel consumption is often several miles per gallon worse than a lower-spec model with 17-inch wheels because the engine has to work harder to turn the larger wheels. .

Your vehicle's electrical system uses the energy generated by the engine. The more of this equipment you turn on, the harder the engine must work, which means the worse the fuel economy will be. Air conditioning, in particular, can have a big impact. Turning off unnecessary equipment will improve fuel economy.

But by far the best thing you can do to make sure your car is getting as many miles per gallon as possible is to service it regularly. If your car's engine is out of order and out of order, it simply won't be able to give you the best MPG.

Can the way I drive affect my car's MPG?

The way you drive can have a big impact on your car's fuel economy, especially if your car has a manual transmission.

Rough engine speeds and high-speed shifting will worsen fuel economy. The higher the engine speed, the more fuel it uses.

Likewise, running too low an RPM and shifting gears too early can degrade fuel economy. This is because the engine has to work harder to get the car up to speed. If you are a cyclist, you may have experienced how difficult it is to move off when your bike is in a high gear. This principle applies to cars as well.

Every engine has a sweet spot where it provides the best balance of performance and fuel economy. This place is different in every engine, but you should be able to find it quite easily. Automatic transmission vehicles are designed to always operate within their sweet spot.

Most modern cars have an "eco" driving mode that you can select at any time. It modifies engine performance to optimize fuel efficiency.

Which cars give the best MPG?

In general, the smaller the vehicle, the better its fuel efficiency will be. But that doesn't mean big cars can't be economical.

Many larger vehicles, especially diesels and hybrids, deliver excellent fuel economy, such as 60 mpg or more. If we take 45 mpg as a reasonable measure of good fuel economy, you can find any type of car that gives you that while still meeting your other needs.

Cazoo offers a wide range of high quality used vehicles. Use the search function to find the one you like, buy it online and have it delivered to your door or pick it up at your nearest Cazoo customer service center.

We are constantly updating and expanding our range. If you can't find one today, check back soon to see what's available, or set up a stock alert to be the first to know when we have cars that match your needs.