I’m sure you’ve seen the phrase “wh/mi” being thrown around on various electric car forums or in articles written about electric vehicles. White House missing? Wheels to miles? No, “wh/mi” actually stands for “watt hours per mile.” Put more succinctly, it is the number of watt hours of electricity a car consumes to travel distance of 1 mile. But what exactly is a watt hour?

I’m the first to admit that I’m not a “science” person. Ever since I got that C in Chemistry class during my sophomore year of high school, I’ve tried to avoid the various scientific disciplines. That being said, I will attempt to tackle this one. Please feel free to correct any errors I make in the comments section.


Back to watt hours. A kind gentleman whose intelligence far exceeds my own by the name of Martin Camacho provides us with this definition:

A Watt Hour is a unit of measurement for power over a period of time (an hour). One Watt hour is equal to one Watt of average power flow over an hour. One Watt over four hours would be four Watt Hours of power. 

A Watt, the measure of power, is usually calculated using this equation: Watts = Volts x Amps. To explain a little further, we will use a plumbing analogy. If we have a water pipe; Volts would be a measure of the water pressure (force) in the pipe, Amps would be a measure of the current or flow through the pipe. A Watt would be the measure of of what you can do with that water, like turning a water wheel. So, how do we determine Watt hours?

Watt Hours are calculated using a similar equation when dealing with batteries. The Equation to find the Watt Hours of a battery gives us a universal measurement.”

Clear as mud? Well, you don’t necessarily need to understand the details in calculating wh/mi to understand why the concept is important.

When the Government Gets Involved  

In 2010, the Environmental Protection Agency (EPA) in conjunction with the National Highway Traffic Safety Administration (NHTSA) decided that all electric cars needed to have a miles per gallon of gasoline equivalent or MPGe. Similar to the way new gas-guzzlers display the amount of miles that can be traveled on a single gallon of gas on their stickers, electric cars display their MPGes in wh/mi.

The EPA uses the wh/mi measurement to evaluate electric vehicles by energy consumption and range. Therefore, it is just as important for electric vehicle owners to know how many wh/mi their cars can achieve as it is for a driver of a conventional car to know how many miles per gallon their car gets. By knowing your car’s wh/mi capabilities, you can maximize performance as well as minimize electricity payments.

That’s what I call a win/win!

What do our readers think about the wh/mi measurement in relation to electric vehicles? Is it important for electric vehicle owners to know and understand these figures? Please leave us a comment below and let us know.

Source | Image: Consumer Reports