How to Calculate Horsepower and Torque for a Hybrid Car

Horsepower for a hybrid is the amount of force that it takes to move an object of 550 pounds that is on a pulley, one foot into the air during one second.  For instance, if a car can lift an object of 1100 pounds, one foot into the air during one second, it has two horsepower.  The torque is a measure of the force that is required to rotate an object on its axle.

How to Calculate Horsepower and Torque for a Hybrid Car? Torque is a twisting motion that spins the axles in a hybrid. It is calculated by using the following formula: Torque=(I*V*E*60)/(rpm*2π).  How fast that torque spins the axles is represented by the rotations per minute or the rpm. Horsepower is (V*I*Eff)/746.

The above explains the formulas in simple terms. I will now go into more detail by using examples for a hybrid.

A formula that calculates Torque for a Hybrid

When you are calculating the torque that a hybrid produces, you need to understand clearly what is happening.  In a gas vehicle, the pistons that are pressing down on a lever which creates the torque.  It is a different story in the electric motor in a hybrid.

image from video on brushless dc motors and control by DigitalPimple

There is no piston in the electric motor of a hybrid car.  How is the force generated to spin the axle?  The concept was confusing for me at first, but I learned that it is a combination of the current that is being provided by the battery pack and the fixed magnets in the motor that causes the spinning to occur.  The combination of these two entities is creating the force.

For calculating the torque, it was hard to find a formula for the electric motor that did not use horsepower, but I finally found one:


I:  current, measured in amperes

V: voltage, measured in volts

E: efficiency, usually provided by the manufacturer as a guaranteed percentage

rpm: rotations per minute

π: 3.14

What is good about the above formula is that the required information is usually given by the manufacturer.  Sometimes there is also a metal tag on the side of the electric motor that highlights the above variables.

I did find a lot of examples of formulas for calculating the torque, but they tended to use the variable horsepower.  Since you are reading this article to find out how to make the calculation for torque and for horsepower, I wanted to make sure that you could do so without having to use the value horsepower that is given by the manufacturer.

What is important to know about calculating torque is that increasing the voltage, amps, or the rotation per minute is going to increase the torque.

A formula that calculates Horsepower for a Hybrid

To calculate the horsepower for the electric motor in a hybrid, you need to know the efficiency, the current, and the voltage.  These values need to be multiplied together.  The resulting value must then be divided by 746.

Horsepower for an Electric Motor:  (V*I*Eff)/746

V: voltage

I: current

Eff: efficiency, a value provided by the manufacturer

For example, if you had an electric motor that was 560v, and it pulled 8 amps, and its efficiency level was at 78%, the horsepower would be

Horsepower = (560 x 8 x .78)/746

Horsepower = 4.68

Before I explain the differences between horsepower and torque for a hybrid, you need to understand that there will also be a value for torque and horsepower due to the gas motor in a hybrid that uses pistons.

The formula for calculating the torque in the gas engine of a hybrid is the following:

torque =  rFsin(θ)

r: the distance between the point of origin on the axis and where the force is applied on the piston

F: linear force, via the piston

θ: this is theta, and it is the angle between where F occurs, and r

The formula for calculating the horsepower in a gas engine in a hybrid is the following:

horsepower = torque x rpm

You need to add together the torques and horsepowers for a hybrid

Since in most cases, a hybrid can use both engines in parallel, you need to total the two torque amounts and the two horsepower amounts.

What are the major differences between Horsepower and Torque for a Hybrid for the electric motor?

I will explain the differences between horsepower and torque in a general sense it will also apply to hybrid cars.  First of all, you need to view horsepower as power and to view torque as a force that is applied to the axles.

More Power Increases Quickness

The more power that is applied to a car, the faster it is going to go over a certain distance.  For instance, if you have two cars that are the same in weight and size, the car that has the most horsepower is going to be to win out.  It is going to be able to move faster over a certain distance.

Some people feel that if you have a ton of torque, your car is going to be super powerful.  Another way to view the torque is to conceptualize it as the muscle in the car.  A bigger muscle is going to be stronger and when it is used, it is going to do some damage to its environment.  If a muscle is just sitting there and not flexing, it is still strong but it is not applying any force.

Force Is Needed to Start the Spinning of the Axles

To use its force, your hybrid electric motor needs amps and current, and it needs to start to spin the axle.  It has to continue to do so, but as the axles spin faster and faster, the amount of force applied can be less and less.  In the beginning, lots of force needs to be supplied so that the axle starts to spin.

When a Vacuum Cleaner Dims Your Lights

I read somewhere that to understand this concept, think about a vacuum cleaner.  Sometimes, when you first start up the vacuum, your lights that are using the same electrical circuit will dim.  This is because a lot of force needs to be applied to start the vacuum’s engine.  After a short period of time, the lights will go back to normal since less electrical juice is required to run the motor or the engine in the vacuum.

When looking at the formula above for torque for the electric motor, you need to divide by rpm multiplied by 2π, which means that the faster the rpm, less force is exerted to spin the axles.

Horsepower Has its Limits

This force is in a sense, altered by the presence of rotations per minute.  Horsepower is not limited by this amount. You do not see the rpm mixed into its formula that I had added above for electric motors.  Nevertheless, horsepower is limited by the amount of amp and current that is used. The other factor that sets a limit to the horsepower, is the efficiency level that is usually provided by the manufacturer.  The more inefficient, the lower that the horsepower amount will be.

You are probably saying to yourself, why not just create an electric motor that uses extremely high amps and current, since those values affect the level of torque and horsepower.  That sounds reasonable, but it would be difficult to design an engine that could deal with extremely high power and force levels.

What Would Happen if we had Massive Torque and Horsepower?

The motor that could deal with super high rpm, amps, and current is hard to design presently.  Also, if a car is too powerful, driving such as vehicle would be difficult.  Imagine trying to control a vehicle that could reach 60 miles per hour in a fraction of a second? You need some sort of android to drive that vehicle safely! If you were to try to drive it, you would probably pass out right away because of the high g forces.

Is the Horsepower higher on a Hybrid than that of a Regular Car?

I have noticed that some manufacturer love to point out how their hybrid models can reach very high levels of horsepower.  What they tend to do is to add together the horsepower from the electric engine and from the gas engine.  I hate to be the bearer of bad news, but using both engines at their highest levels of horsepower is rarely possible.

Does the Typical Hybrid Driver Really use the Full Horsepower?

It is as if they are not lying to us, but I would consider highlighting those high horsepower amounts is misleading, to say the least.  Most hybrid owners that are driving within a city will rarely be using both engines at the same time.  Maybe on a trip that requires the highway.

Why doe a Hybrid Feel So Powerful Even While Accelerating in the City?

If you are just going by the feel, even in the city, you will notice right away that as soon as you press on the accelerator that the hybrid car has some power behind it.  It is nothing like the initial blastoff in a normal car. In your mind, you are probably surmising that your car is full of thousands of horses.  It is just the torque that you are sensing because is maxed out in the beginning with the set amount of amps and current that is being supplied by the electric battery pack.

You Need to Aware of the Efficiency Level

Also, I have noticed that in manuals, the efficiency level is stated as the maximum efficiency level.  It would better if they were to state is as the average efficiency level.  Since torque and horsepower both use the efficiency level in their formulas, you need to use a percentage that is reasonable and not too lofty.

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