Octopus Electric Vehicles Logo
A graphic of Constantine the Octopus in an EV next to a broken down fuel car
  • Nov 7, 2022

  • 6 min read


Are electric vehicles more efficient than fuel-burning cars?

One of the main reasons that EVs are booming in popularity is their reduced impact on the environment compared to fuel-burning cars.

But just because EVs don’t emit exhaust fumes as they drive, are they more efficient than fuel-burning rivals? We investigate how to calculate electric car efficiency and how that compares to fossil fuel cars.

How is efficiency measured in electric cars?

First off, what do we mean by efficiency? A car’s fuel efficiency is how far it gets you on the fuel it has in its tank. In an EV it affects how far you can travel on a full charge.

Car manufacturers measure electric car efficiency in a couple of ways. The simplest way is to find out how much energy the battery can hold. This is measured in kilowatt hours (kWh). Then you can look at the car’s official range. If it has a 50kWh battery and its range is 150 miles, it’ll cover 3 miles per kWh.

Here’s the maths: EV range ÷ kWh battery size = miles per kWh.

In simple terms, the higher the miles per kWh the more efficient the battery. Our 3 miles per kWh figure above is pretty average; and the most efficient electric car will return about 5 miles/kWh.

Still with us? Good.

Sadly, it’s too simplistic to say a longer range electric car is more efficient. A big car with a larger, heavier battery may well go further on every charge. But its lighter rival with the smaller battery will probably be more efficient, even though it won’t cover as many miles per charge. This is because it’s likely to use less energy per mile that it covers.

How efficient are electric cars compared to petrol or diesel?

EVs are pretty similar to petrol models in that the smaller and lighter the car, the more energy efficient it's likely to be. Where EVs beat fossil fuel cars hands down is in the electric car motor efficiency. Electric car motors are much better at converting the energy they’re supplied with into movement than combustion engines.

Although petrol and diesel engines have undergone remarkable improvements over the years, they’re still pretty inefficient. This is because they have to operate at high temperatures meaning a lot of the fuel’s energy is wasted in friction, heat and noise.

Greenpeace says the most efficient petrol engines only convert 12-30% of the energy in their fuel into making the car move, or other useful functions. In contrast, electric cars are around 77% efficient by the same measure. This means you'll get more than twice as many miles out of the same amount of energy.

At what speed is an electric car most efficient?

Now, before you go racing off (see what we did there), stick around for a bit and learn some facts with us.

As with any car, an EV’s efficiency changes all the time depending on how you drive, the road you use and even the power of the wind. Battery efficiency also depends on outside temperature: in extremes of heat and cold, batteries deliver fewer miles per kWh.

The power needed to move any car increases as the speed goes up. The faster a car goes, the more energy it needs to overcome the resistance of the air it has to push aside. This is known as drag.

Petrol cars are most efficient at speeds around 50mph. Faster than that and drag has an impact; slower and the engine isn’t working at optimum efficiency.

This is completely different with EVs. Unlike combustion engines, electric motors only have a single gear. That means they don’t have to be at a certain speed to run at maximum efficiency. But the faster they go, the more energy they still need to overcome increased wind resistance, so lower speeds are more efficient.

Obviously you can’t drive everywhere at 10mph. But if you’re in an urban setting and the speed limit is 20mph, you’re onto a winner: slow and steady maximises your EV’s efficiency meaning you’re getting the maximum number of miles from your charging.

How to make electric cars more efficient

There are lots of ways you can boost your EVs driving range so that you’re getting the most miles out of your electric car. Here’s a few ways you can improve your car's efficiency.

Reduce the weight of the car

We’ve seen the negative effect wind resistance can have on how far an electric car can travel on a single charge. Car designers spend many hours sculpting the shape of their cars to be as aerodynamic as possible. Put a roof rack or roof box on and all that hard work goes down the drain.

Meanwhile other engineers are working just as hard at shaving grams off the car’s weight. The heavier a car is, the more energy it takes to move it. So make sure you’re not carrying any unnecessary weight.

Keep your tyres inflated

Our next focus is on the tyres. Car manufacturers specify the optimum inflation pressures for maximising energy efficiency. At lower inflation pressures, more of the tyre is in contact with the road so the motor needs more energy to keep it rolling. It’s a bit like the extra effort it takes to pedal a bike with flat tyres.

Switch off unnecessary features

Now consider your comfort. A lot of battery energy is needed to heat and cool a car. If you can, use your car’s pre-conditioning feature. This allows you to heat or cool it while it’s still plugged in. Then keep your air con or heating turned as low as possible to reduce the energy draw and maximise the amount of battery power used to move the car.

If you’re looking for more ways to get the best efficiency out of your car, check out our top tips on how to maximise your EV range.

And if you want to find the most efficient electric cars on the market make sure to check out our long range EV makes and models.