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Miles per kWh – the new MPG

When you get a petrol or diesel car, you want to know how many miles per gallon it does. The higher the MPG figure, the less money you have to spend on fuel.

So what’s the equivalent of MPG for an all-electric car? Instead of miles per gallon, it’s 'miles per kWh' (pronounced kilowatt-hour).

In this quick jargon-busting guide, we explain everything you need to know about this new efficiency metric for electric cars.

Miles per kWh definition

With a traditional car, the MPG number tells you how many miles the car will go on 1 gallon of petrol or diesel.

In an electric car, the miles per kWh figure tells you how many miles the car will go on 1 kWh, or unit, of electricity. 

So if your EV has a battery size of 50 kWh and an efficiency rating of 3 miles per kWh, then on average it can travel 150 miles on a fully charged battery (50 kWh x 3 miles per kWh).

What if the miles per kWh figure is not displayed? Just take the battery range of the car and divide by the battery size. So an EV with a 240 mile range and a battery capacity of 60 kWh would have an efficiency rating of 4 miles per kWh (240 ÷ 60).

What’s a good miles per kWh number?

Now we all know that 50 MPG is a pretty good efficiency rating for a normal car and that 15 MPG would be poor. But what about electric cars? What’s a high number and what’s a low number?

The highest efficiency electric cars today achieve 4 miles per kWh or above. For example, both the Tesla Model 3 Standard Range Plus and the Fiat 500e enjoy excellent battery efficiencies.

A very low efficiency figure would be 2 miles per kWh. Some of the early electric cars that came out 8-10 years ago weren’t great at converting stored battery energy into actual miles driven.

Nowadays, most electric cars have a real-world efficiency of at least 3 miles per kWh, though a few dip down to around 2.5 miles per kWh.

Understanding miles per kWh

  • Efficiency in an EV is measured as ‘miles per kWh’ 
  • Very efficient electric cars are 4 miles per kWh or higher; less efficient ones are around 2.5 miles per kWh
  • Most all-electric cars are at least 3 miles per kWh 
  • You may also see efficiency displayed as 'Wh per mile' or 'Watt-hours per mile' – just divide the number into 1,000 to convert to 'miles per kWh', e.g. 250 Wh per mile = 4 miles per kWh

What does a high miles per kWh rating mean in practice?

Having a high miles per kWh rating is all about saving money.

Imagine your EV can do 4 miles per kWh and you drive 8,000 miles a year. How much electricity do you need to cover that distance?

It’s 8,000 miles divided by 4 miles per kWh which equals 2,000 kWh (or 2,000 units of electricity).

If you charge at home on an off-peak tariff of say 8p per kWh, those 2,000 kWh will cost you £160 (2,000 kWh x 8p). 

Now compare that with a car that can do only 3.2 miles per kWh. You’ll need more electricity to cover the same 8,000 miles. The calculation is: 8,000 miles divided by 3.2 miles per kWh = 2,500 kWh. Charging at home at a rate of 8p per kWh would therefore cost you £200 (2,500 kWh x 8p). 

In the less efficient 3.2 miles per kWh car, you end up paying 25% more on electricity to go 8,000 miles. In absolute terms, it’s only £40 extra a year, so still very good value when compared to a petrol or diesel car.

Want to discuss leasing an electric car?

Why not phone us on 0118 920 5130 or email at enquiries@selectcarleasing.co.uk

Miles per gallon equivalent – comparing efficiencies

There’s a handy way of quickly comparing how efficient electric cars are compared to traditional cars.

Just take the miles per kWh figure and multiply by 40. So an efficient 4 miles per kWh electric car is the equivalent of a 160 MPG car. 

Even a relatively inefficient electric car offering 2.5 miles per kWh would be the equivalent of 100 MPG in a petrol or diesel car. 

The ‘multiply by 40’ rule of thumb gives you a quick, rough equivalent for electric vehicles in the UK. It won’t yield exactly the right figure, as there are many variables in play, but can give you a general indication of how efficient all-electric cars are compared to petrol and diesel powered vehicles.

The most efficient electric cars in 2021

Here are the top 10 most efficient electric cars to lease in terms of miles per kWh:

  1. Tesla Model 3, Standard Range Plus: 4.56 miles per kWh
  2. Fiat 500e: 4.54 miles per kWh
  3. Tesla Model 3, Long Range: 4.54 miles per kWh
  4. Hyundai Ioniq Electric: 4.19 miles per kWh
  5. BMW i3: 4.16 miles per kWh
  6. Mini Electric: 4.10 miles per kWh
  7. Seat Mii electric: 4.10 miles per kWh
  8. Volkswagen e-up!: 4.07 miles per kWh
  9. Smart EQ fortwo: 4.05 miles per kWh
  10. Hyundai Kona Electric (39 kWh): 3.99 miles per kWh

Miles per kWh figures are approximate and will vary according to ambient temperature, speed and other factors. The efficiency data are based on estimates of average, real-world range (roughly official WLTP range minus 18%) and useable battery capacity.

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