Making sense of electric car efficiency

electric car efficiency guide

Electric cars are surging in popularity thanks to their reduced environmental impact compared to petrol-powered cars. But are they actually more efficient?

As EV adoption grows, it’s important to understand exactly how efficiency works and how to maximise it. This guide breaks down the key factors.

What Does “Efficiency” Mean for EVs?

For any car, efficiency refers to how far it can travel per unit of energy. For EVs, that means miles per kilowatt-hour (kWh) – the more miles, the better. Manufacturers calculate this using battery capacity and range. A car with a 50 kWh battery and 150 mile range covers 3 miles per kWh (150 divided by 50). The most efficient EVs today achieve around 5 miles per kWh.

However, longer range doesn’t always mean better efficiency. A larger, heavier battery may enable more miles per charge but use more energy per mile. The lightest EVs tend to be the most efficient thanks to lower energy needs.

Miles per kWh – The EV MPG

Just as miles per gallon (MPG) measures efficiency in a combustion-powered car, miles per kilowatt-hour (kWh) serves the same purpose for electric vehicles. The more miles a car can travel using 1 kWh of battery capacity, the better its efficiency.

For example, if an EV has a 50 kWh battery pack and can drive 150 miles on a full charge, it is operating at 3 miles per kWh (calculated by dividing the range by the battery capacity).

This is directly comparable to mpg for internal combustion engine vehicles. A higher miles per kWh number indicates greater efficiency, just like a higher mpg translates to using less gas to travel the same distance. It’s an at-a-glance way to understand how well an electric car converts energy into real-world range.


Another way to calculate electric car efficiency is Wh/mi, or watt-hours per mile – if you have a Tesla, you will be familiar with this because Tesla cars use it.

What’s the difference between Wh/mi and miles per kWh? Wh/mi refers to the energy consumption of the electric vehicle – specifically, how many watt-hours or kilowatt-hours of battery energy are used to travel one mile. Lower numbers indicate greater efficiency – this is the opposite of miles per kWh, where higher numbers indicate greater efficiency.

Miles per kWh refers to distance travelled per unit of energy used from the battery. So it represents range divided by battery capacity.

They are reciprocal metrics. For example, if an EV has a consumption of 250 Wh/mi, then it travels 1/250 miles per 1 Wh. Invert that and you get 4 miles per 1 kWh (4 mi/kWh). So in summary:

  • Wh/mi – Energy use per unit of distance
  • Lower = more efficient
  • Miles per kWh – Distance per unit of energy
  • Higher = more efficient

Looking at either metric allows you to compare the efficiency and expected range of different electric vehicles.

Electric vs combustion: Which Wins on Efficiency?

Thanks to major advances, petrol engines now convert 12-30% of fuel energy into motion. Impressive, but electric powertrains have tractive efficiencies ranging from 82% to 93% according to a study by SAE.

That’s over twice as efficient – the same energy takes you more than twice as far. Size and weight still matter (there are concerns that electric cars are getting too big), but EVs generally beat equivalent petrol and diesel models.

Understanding Speed and Efficiency

Speed significantly impacts EV range. Air resistance increases with speed, requiring more power to push through. Petrol cars are typically most efficient around 50 mph – slower and their engine runs sub-optimally; faster and drag hinders them.

But most EVs have a single gear so maintain peak drivetrain efficiency at any speed. Below 50 mph, they outperform petrol cars by an even greater efficiency margin.

Slow urban speeds like 20 mph maximise miles per kWh. However, real-world conditions like cold weather can reduce battery performance.

What Are The Most Efficient Electric Cars?

According to the latest figures from EV Database, the six most efficient electric cars are the:

  1. Tesla Model 3 (221 Wh/mi, 260 mi range)
  2. Hyundai IONIQ 6 Long Range 2WD (243 Wh/mi, 305 mi range)
  3. BMW i4 eDrive40 (252 Wh/mi, 320 mi range)
  4. BMW i4 eDrive35 (253 Wh/mi, 265 mi range)
  5. Peugeot e-208 51 kWh (253 Wh/mi, 190 mi range)
  6. Renault Megane E-Tech EV60 220hp (255 Wh/mi, 235 mi range)

The Tesla Model 3 is the most efficient with 221 Wh/mi energy consumption and 260 miles of range. The Hyundai IONIQ 6 places second with 243 Wh/mile efficiency and a 305 mile range. The BMW i4 variants take third and fourth, followed by the Peugeot e-208 and Renault Megane E-Tech EV60 as other high efficiency options.

Optimising Your EV’s Efficiency

Follow these tips to squeeze more miles out of a charge:

  • Minimise weight: Roof racks and unnecessary cargo make the motor work harder. Save pounds to save energy.
  • Inflate tires properly: Underinflated tires increase rolling resistance on the road, dragging on efficiency. Inflate to the manufacturer recommendation.
  • Limit climate use: Heating and AC drain battery power. Employ preconditioning while plugged in to warm/cool the cabin beforehand when possible.
  • Reduce energy draw: Turn off seat heaters, music and accessories when not needed to route power to the motor over creature comforts.

As EV makers push the boundaries of aerodynamics, weight savings and powertrain tech, efficiency will only get better. And drivers can benefit from every advance by adopting savvy driving and charging habits. When both parties focus on maximising miles per kWh, it’s a win for efficiency and the wallet.

James Lewis is our resident electrical head. He drives an MG ZS EV (2018, which he loves) and plans to get the new one soon. James is much more excited by the lower end of the EV market and is looking forward to the Ora Cat.