How Is Horsepower Calculated?

Calculate Torque

Find out the torque of your engine. You'll need access to a dynamometer or "dyno" for short. Only a professional dynamometer technician can operate these. Normally, this involves locating and scheduling an appointment with a shop or garage that has a dyno in-house. Your vehicle is put on a flat bed with a rotating wheel underneath your vehicle's drive wheels. As you accelerate the vehicle on the dyno, your vehicle remains stationary and the dyno wheel spins, measuring the power output and torque of your vehicle. Once the technician has calculated the torque for your vehicle, make note of this number.

Multiply Torque by Engine Speed

Multiply the torque number by the engine speed. You should have both of these numbers given to you by the dyno technician. Torque will be relative to the rate at which your engine is spinning. For example, if your torque is 300 pound-feet, there will be an associated revolutions per minute, or "RPM," associated with your torque number. So, for example, your engine may be producing 300 pound-feet of torque at 4,000 RPM.

So, using this example, you'll need to multiply 300 x 4,000 = 1,200,000.

Divide by 5,252

Divide by 5,252. This number is derived from a series of conversion factors which are added together into this one number.

Continuing the example above, the equation would look like this:

(300 x 4,000) / 5,252 = 228.48

You can round this number off. So, for example, instead of using 228.48, you could round it off to 228. This number represents horsepower.

References

• Torque & Horsepower--A Primer
• Horsepower vs. Torque
• A Technical Discussion of Torque and Horsepower