How can we compare how efficient an EV is vs an ICE vehicle? Let’s talk about efficiency today and see how the measurements of MPG and MPGe are calculated!
Photo by Jp Valery on Unsplash
Many websites, like for instance fueleconomy.gov provide comparisons of eficiency between ICEs and EVs, and EVs are clearly the winners here (sorry, spoilers! 
) but do you know how those figures are calculated? Let’s dive in! 
The cost of petrol
According to AA, the average petrol cost in March 2024 (last time they reported on this) was £1.46 per litre in London, which means £6.64 per gallon.
For ICE vehicles, we typically use the MPG, or Milles per Gallon, which is a common measurement of fuel economy. It represents the average number of miles a vehicle can drive on one gallon of fuel. A reasonable average for MPG for a newer ICE is 45.
For EVs, we measure in miles-per-gallon equivalent (MPGe) so we can compare similar figures. In terms of energy, 1 gallon of gasoline is equivalent to 33.7 kWh. I hope you are still with me! 
How do we compare these two figures to understand what’s the running cost per mile for an EV vs an ICE vehicle?
Going back to our previous numbers, with £6.64 and an average ICE, we are able to drive for 45 miles. Which means 1 mile will cost us 15p (£6.64/45miles)
The equivalent cost for an EV
Let’s take the Tesla model 3 as an example, we can find on fueleconomy.gov that it needs 26 kWh per 100 miles.
Let’s calculate! 
- Distance: 100 miles
- Energy consumption: 26kWh
- Convert to equivalent gallons: 26 kWh / 33.7 kWh/gallon = 0.77 gallons
- MPGe = 100 miles / 0.77 gallons = 130 MPGe
How much would it then cost to drive one mile in a Tesla model 3? If you were paying electricity at the cost of £6.64 per gallon of petrol, that would then cost you 5p (£6.64 / 130 miles)
But how much is that in electricity?!
Ok, I hear you, it’s now best if we also check how much this actually costs us in electricity.
Using as an example a UK tariff that charges 7p/kWh:
- Total cost to charge to drive 100 miles: 26kWh * 7p/kWh = £1.82
- Cost for 1 mile: £1.82/100 miles = 2p
So with a 7p tariff, the cost per mile with an EV (2p) more than 7 times cheaper than with an ICE (15p)!
Using as an example a UK tariff that charges 15p/kWh:
- Total cost to charge to drive 100 miles: 26kWh * 15p/kWh = £3.9
- Cost for 1 mile: £3.9/100 miles = 4p
With a 15p tariff, the cost per mile with an EV (4p) almost 4 times cheaper than with an ICE (15p)!
We can only expect to see the MPGe of EVs increase as better batteries are developed, and the technology and infrastructure gets more stablished. Onwards!