- Miles per kWh measures energy efficiency in electric vehicles.
- Miles per kWh tells you how many miles an EV travels for every kWh it consumes.
- Very efficient electric vehicles return over 4.2 miles per kWh.
- Miles per kWh can also be shortened to kWh/miles and mi/kWh.
With a combustion-engine vehicle, we measure fuel economy in miles per gallon (mpg) which tells us how many miles it can travel for every gallon of fuel it burns. Electric vehicles don’t burn petrol, but they do consume electricity stored in their batteries, so we measure energy efficiency in miles per kWh.
Miles per kWh
Miles per kWh is the number of miles an electric vehicle can travel on 1 kWh of battery energy. The more miles per kWh an EV can achieve, the less energy it requires to travel a given distance and the further it can go before needing to be recharged. For example, if an electric car is rated at 4 miles per kWh, that means it can travel 4 miles using just 1 kWh from its battery pack. The miles per kWh number is affected by various factors like the vehicle’s weight, drag, rolling resistance, drivetrain efficiency and auxiliary power draw. A higher miles per kWh value is better, as it equates to using less energy and getting more range from the EV’s batteries. It allows direct comparison of the relative energy efficiencies between different vehicles.
In this guide, we’ll discuss electric car energy efficiency in detail to help you transition from a miles per gallon mindset to a miles per kWh one.
What is a kWh?
Let’s start with the basics.
In an electric vehicle, kWh is the total amount of energy stored in a battery. It is not the amount of energy you consume in an hour.
When an electric vehicle is driven, it consumes energy stored in the battery. That consumption is measured in miles per kWh. Miles per kWh measures how many miles the vehicle can be driven with 1kW of energy.
What is miles per kWh?
Miles per kWh (kilowatt-hour) is a measure of the energy efficiency of an electric vehicle. Specifically, it refers to the number of miles an electric vehicle can travel on one kWh of battery energy.
A few key points about miles per kWh:
- It allows for comparing the energy efficiency of different electric vehicles. The higher the miles per kWh rating, the more efficient the EV is.
- It is affected by vehicle weight, aerodynamics, terrain driven, auxiliary loads (A/C, heat), and driving style. Light and aerodynamic vehicles tend to have higher miles per kWh.
- Environmental conditions like ambient temperature also impact miles per kWh, with colder weather reducing efficiency.
- Most modern electric cars today achieve efficiency in the range of 3-6 miles per kWh. So traveling 100 miles would use roughly 17-33 kWh from the battery.
- Improving miles per kWh through better design allows EVs to travel farther on a single charge. So it’s an important metric for developing longer-range electric vehicles.
Miles per kWh is an extremely useful metric because it tells us the efficiency of the electric vehicle and lets us calculate range (more on this below).
In the image below, we’ve circled the miles/kWh rating for the VW ID 3:
What is a good miles per kWh?
Great efficiency is above 4.2 miles per kWh, good efficiency is above 3.8 miles per kWh, and average efficiency is anything above 3.5 miles per kWh:
- Great – Above 4.2 miles per kWh
- Good – Above 3.8 miles per kWh
- Average – Above 3.5 miles per kWh
The kWh figure for today’s EVs tends to fall between 3.5-4.5. This means an EV could travel 3.5-4.5 miles for every kWh of battery energy consumed. The most efficient EVs currently achieve 4-4.5 miles per kWh under optimal conditions.
However, real-world efficiency varies widely based on driving style and conditions. Aggressive acceleration and high speeds can reduce efficiency by 30% or more. Cold temperatures can sap another 10-35%. Choosing smaller wheel options with low-rolling resistance tires makes a surprising impact too – improving economy by 5% or more.
On the vehicle design side, lightweight construction plays a major role. Reducing vehicle curb weight directly correlates with better mileage per kWh since less energy is required to move the mass.
For example, the Tesla Model 3 weighs 1000lbs less than the Model S or X SUVs, contributing greatly to its class-leading efficiency. Integrating the motors, electronics and batteries into the chassis also helps by eliminating separate transmission and drive line components.
Aerodynamic optimisation is just as critical. Minimising the drag coefficient with slippery shapes cuts energy use at highway speeds. Tesla again leads among production EVs with a drag coefficient around 0.23, on par with high-end sports cars.
Lastly, maximising regenerative braking efficiency when slowing down helps put wasted kinetic energy back into the battery. This “one-pedal driving” offered in some EVs like the Nissan Leaf plays a role in optimising miles per kWh.
What is Wh/mi?
Wh/mi stands for watt-hours per mile. It gives you the same efficiency rating as miles per kWh but with a higher number.
- 1 KWh = 1000Wh
- Wh/mi: How much energy you use every mile measured in watt-hours
There are 1,000 watts in 1 kW, so when you see efficiency rated in Wh/mile, you can divide 1,000 by the Wh/miles figure to get the miles per kWh. For example, 1,000 divided by 235Wh/mile is 4.255 miles per kWh:
1,000 (watts) / Wh/mile = miles per kWh
E.g., 1,000 divided by 235Wh/mile is 4.255 miles per kWh
Is Wh/mi better than miles per kWh?
Wh/mi (watt-hours per mile) and miles per kWh (kilowatt-hours) are essentially two ways of measuring the same thing – the energy efficiency of an electric vehicle. But there are some minor differences between the metrics:
- Wh/mi measures the electrical energy consumed per mile. Lower numbers indicate higher efficiency. Miles per kWh measures miles travelled per unit of energy, so higher numbers indicate better efficiency.
- Wh/mi is more commonly used in the United States, while miles per kWh is favored in Europe and elsewhere. They are reciprocals of each other.
- Miles per kWh has a slightly larger numerical value. For example, 3 miles per kWh equals 333 Wh per mile. This makes comparing efficiency across vehicles a bit easier.
- Miles per kWh better accounts for the total energy drawn from the battery. Wh/mi only measures net energy consumed per mile and does not capture electrical losses that ultimately reduce range.
So in essence, both metrics are valid ways to quantify EV energy economy. But miles per kWh paints a more complete picture by reflecting total battery energy usage rather than just net consumption. It avoids the need to account for charging and electrical losses separately.
This gives miles per kWh a slight edge for comparing overall energy efficiency in practice. Either metric serves the purpose, but miles per kWh translates more directly to real-world driving range.
How to calculate range using miles per kWh
To calculate range using miles per kWh, all we do is take the available battery capacity (kWh) and multiply it by the vehicle’s miles per kWh:
40kWh (battery capacity) x 3.6 miles per kWh = 144-miles
Now, electric cars aren’t 100% efficient, so let’s deduct 10% off our calculation to account for energy loss and poor road conditions:
40kWh (battery capacity) x 3.6 miles per kWh – 10% = 129.6 miles
The second figure is more realistic for real-world conditions.
You can also calculate charging time by dividing the vehicle’s battery capacity by the charging point’s charge rate. Here’s the formula:
Battery Capacity ÷ Charge Speed = Charge Time
Estimated and real-world miles per kWh
Like miles per gallon, miles per kWh has an estimated (manufacturer) figure and a real-world (driver) figure:
- Estimated miles per kWh: Estimated miles per kWh is provided by the vehicle manufacturer based on testing data under WLTP conditions
- Real-world miles per kWh: Real-world miles per kWh is what the driver achieves on the road, and this is always different to the estimate
In our experience, the estimated kWh is 20% less than the real-world kWh figure in all conditions. So, if a manufacturer says you’ll get 3.9 miles per kWh, assume you’ll get around 3.12 miles per kWh.
The reason estimated and real-world efficiency is different is because electric vehicles are tested under Worldwide Harmonized Light Vehicle Test Procedure (WLTP) conditions, which are not completely realistic.
What factors affect miles per kWh?
Vehicle weight
Vehicle weight has a significant impact on electric vehicle efficiency. Heavier vehicles require more energy to accelerate and maintain speed due to basic physics. The heavier the vehicle, the more friction and inertia it must overcome, putting higher demands on the electric powertrain and draining the battery faster. Automakers use lightweight materials to reduce curb weight, but features added for comfort, passenger capacity, aesthetics or performance can offset those weight savings. Every extra pound reduces the miles per kWh rating.
Ambient temperature
Ambient temperature affects miles per kWh because electrical resistance increases in cold weather. The chemical reactions within lithium-ion batteries happen more slowly at lower temperatures. This means more energy is lost as heat instead of generating movement of electrons to power the vehicle. In very cold weather, large reductions in driving range and efficiency can occur if battery conditioning is not optimal. Some EVs have thermal management systems to warm the battery and mitigate cold weather losses.
Driving style
Driving style significantly impacts efficiency ratings. Electric motors have full torque from 0 rpm, allowing rapid acceleration. But accelerating gently allows the motor to operate at higher efficiency points on its performance curve.
Aggressive acceleration and high sustained speeds put more load on the powertrain. Sports modes tune the vehicle for maximum performance, tapping much more energy from the battery per mile driven, reducing miles/kWh. ECO modes do the opposite, limiting acceleration and top speed to maximise efficiency. Driving style alone can change the rating by 25% or more.
So, to summarise:
- Vehicle weight: More weight requires more energy to move, so heavier electric vehicles have poorer efficiency.
- Temperature: Cold weather saps power from the battery by increasing energy loss between the battery and electric motor.
- Performance: When power and torque is dialled up, electric cars are less efficient because the electric motor draws more energy.
- Driver behaviour: Electric vehicles have Eco and Sport modes. Using the most powerful mode will reduces miles per kWh. Additionally, accelerating hard draws a lot of energy, reducing range and miles per kWh.
kWh to miles
We can also reverse miles per kWh into kWh to miles to find out how many kWh equates to one mile, ten miles, twenty miles, etc.
Here’s how:
- 1 kWh = 3.6 megajoules (MJ) of energy.
- It takes approximately 0.25 MJ to power a typical electric car 1 mile.
- So 1 kWh can power an electric car about: 3.6 MJ / 0.25 MJ/mile = 14.4 miles.
Therefore, the conversion is:
1 kWh = 14.4 miles
So for example:
- 10 kWh = 10 * 14.4 = 144 miles
- 50 kWh = 50 * 14.4 = 720 miles
Each kWh provides enough energy to power the car about 14.4 miles, on average.
How many miles per kWh in an electric car?
Electric cars can achieve anywhere from 2-5+ miles per kWh depending on the vehicle and driving style. On average, most electric cars get 3-4 miles per kWh with normal driving:
- Normal Driving: 3-4 miles per kWh. This applies to typical day-to-day driving with some highway use. It represents a reasonable estimate for most electric cars under normal conditions.
- Aggressive Driving: 2-3 miles per kWh. Hard acceleration and high speeds will reduce efficiency. Expect the lower end of the range with this style.
- Efficient Models: 5+ miles per kWh. Some of the most efficient electric cars like the Hyundai Ioniq 5 can achieve close to 4 miles per kWh in optimal conditions. But this applies primarily to specialised high efficiency models.
So while results vary based on the EV and driving behaviour, a typical range is 3-4 miles per kWh for most electric cars under normal everyday driving conditions. Aggressive acceleration or high speeds will mean fewer miles per kWh. The most efficient EVs can reach 5+ miles per kWh.
Summing up
Miles per kWh (mi/kWh) tells us how many miles an electric vehicle can travel for every kWh of energy it consumes. Vehicle manufacturers publish these figures following WLTP testing to provide an accurate depiction of real-world driving experience.
Multiple factors can affect electric vehicle efficiency, but the main ones are payload weight (such as how many passengers you carry, and towing), temperature, and driving style. Most EVs can achieve over 3 miles per kWh without trying too hard.
