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Horsepower is a unit of measurement that calculates power. It was originally coined by a Scottish engineer to compare the power of steam engines with the power of horses. This article will show you how to calculate the horsepower of your cars engine, an electric motor, and your own body.
Steps
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Get your car’s torque numbers. Look under the “technical specs” section, or look for “torque” in the index of the owner’s manual, and it will give you the torque value. If you do not have the owner’s manual, try using a search engine to find your car’s torque. For instance, search “torque” and your car’s make, year, and model, and a helpful result should come up.
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Find your car’s engine speed. This can also be found in your owner’s manual. If your owner’s manual does not have this information or if you do not have the manual, type your car’s make, year, and model in a search engine followed by the words “engine speed.” An online resource should have this number.Advertisement
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Multiply the torque by the engine speed. You will be using the formula (RPM * T) / 5252=HP, where RPM is the engine speed, T is the torque, and 5,252 is radians per second. The first calculation you want to do is multiply the torque and the engine speed. [1] X Research source
- For example, a Porsche generates 480 of torque at 2,500RPM. Expressed in terms of the equation, that is (2500 * 480), which equals 1,200,000.
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Divide the product by 5,252. The result is your car’s horsepower. In the Porsche example, 1,200,000/5252 = 228.48, so the Porsche has 228 horsepower. [2] X Research source
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Figure out the current (I), efficiency (Eff), and voltage (V) of the motor. The voltage of the motor will be expressed in volts, the current will be expressed in amps, and the efficiency will be expressed as a percentage. The motor should have these units of measurement written on it. [3] X Trustworthy Source U.S. Department of Energy Official site for the U.S. Department of Energy, which provides resources related to energy safety, conservation, and efficiency Go to source
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Using the formula (V * I * Eff)/746=HP, determine your electric motor’s horsepower. Multiply the voltage, the current, and the efficiency, then divide the result by 746. For example, the horsepower of a 230v motor pulling 4 amps and having 82% efficiency would equal 1 horsepower. [4] X Research source
- Convert the efficiency into a decimal before calculating. For example, a 82% efficiency would equal .82.
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Weigh yourself. Find out how much you weigh in pounds. Write your weight down. If your scale uses kilograms, multiply this number by 2.2 to find your weight in pounds.
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Find a stairway that is free from obstructions. You’ll be running up these stairs with a stopwatch, so try to find a stairway that is not frequently used.
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Measure the total height of the stairs. First, find the height of one stair in feet. Then, count how many stairs are in the stairwell you will be running up. Multiply these two numbers, and you will have the total height of the stairs. Write down the height. [5] X Research source
- If your ruler uses meters, multiply the height by 3.28 to convert the measurement into feet. [6] X Research source
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Time how long it takes you to run up the stairs. Get a running start, and when your foot lands on the first step, start your stopwatch. When both feet are on the top step, stop your stopwatch. Write down the duration of your climb to the top in seconds. Remember, there are 60 seconds in every minute.
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Use the formula (m*9.81*h)/t=HP to calculate your watts. In this instance, m = your weight, h = the height of staircase, 9.81 is the gravitational constant that must be taken into account, and t = time (in seconds) of your climb. The resulting number you get is expressed in watts. [7] X Research source
- For example, if you weigh 180 lbs, and climb a 12-foot staircase in 4 seconds, that equals ((180 * .454) * 9.81 * (12 * .3048)) / 4 = 733 watts.
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Calculate your Horsepower. Divide the number of Watts by 746 to find out your horsepower rating. This result is usually between 1-2 horsepower.
- In this example, we can use the formula (m*9.81*h)/t=HP because we are assuming that the only force acting on the runner is the force of gravity.
- Since the only force acting on the runner is the force of gravity, we know that all the horsepower the runner produces is used to push upward (vertically) against gravity.
- We are not accounting for friction, which would normally slow a runner down by exerting a force in the horizontal direction.
- In the real world, a runner would also have to push forward against friction, just as they would have to push upward against the force of gravity. You’d need a more complicated formula to account for friction and gravity together.
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Expert Q&A
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QuestionWhat's the difference between horsepower and torque?Nick Psaros is an Automotive Expert working to encourage people to become car enthusiasts and share useful automotive content with people around the world. He has spent the past six years building an online following and community dedicated to automotive excellence. He has a follower base of over 10,000 YouTube subscribers and has garnered over 1 million views on his channel.Horsepower is a measure of the engine's ability to do work overtime, often associated with a vehicle's top speed and overall performance. Conversely, Torque represents the rotational force produced by the engine, providing the feeling of acceleration. While horsepower influences a vehicle's top speed, torque plays a crucial role in its acceleration and towing capabilities. In essence, torque is the force that propels the vehicle forward, and horsepower determines how quickly it can maintain that force over time. Contrary to common perception, modern turbo engines generate significantly more torque than naturally aspirated ones. This heightened torque delivery improves performance within the RPM ranges commonly encountered in your daily driving.
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QuestionHow can I calculate horsepower from a motor?Community AnswerMultiply the voltage, current and efficiency; then divide the result by 746. For example, the horsepower of a 230 volt motor pulling four amps and having 82 percent efficiency would equal one horsepower. Convert the efficiency into a decimal before calculating.
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QuestionWhat is the horsepower for a centrifugal pump?Community AnswerA pump is not a drive. It will be driven by another source or prime mover such as an engine, motor or natural kinetics. Only the drivers have horsepower, not the pump.
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Tips
- Use a calculator for all multiplication and division operations.Thanks
- Perform calculations twice to make sure you entered them into the calculator correctly.Thanks
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Things You'll Need
- Bathroom scale that measure in pounds
- Ruler
- Calculator
- Stopwatch
- Owner's manual of your car
Expert Interview
Thanks for reading our article! If you’d like to learn more about car maintenance and repair, check out our in-depth interview with Nick Psaros .
References
- ↑ https://www.education.pa.gov/K-12/Career%20and%20Technical%20Education/Resources/Teacher%20Resources/MathTCharts/Math%20TCharts/Automotive%20Technology%20-%20Number%20And%20Quantity%20Dynamometer.pdf
- ↑ https://sciencing.com/calculate-horsepower-rpm-6224196.html
- ↑ https://www.energy.gov/sites/prod/files/2014/04/f15/10097517.pdf
- ↑ https://www.engineeringtoolbox.com/electrical-motor-efficiency-d_655.html
- ↑ http://www.physics.ucla.edu/k-6connection/forwpsa.htm
- ↑ http://www.simetric.co.uk/metres_to_feet.php
- ↑ https://letstalkscience.ca/educational-resources/hands-on-activities/how-much-power-generated-when-climbing-a-set-stairs
About This Article
Article Summary
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It’s easy to calculate a car’s horsepower if you know its torque and engine speed, using the formula RPM (rotations per minute) x T (torque)/5,252 = HP (horsepower). You can usually find the torque numbers listed in the technical specs section of your owner’s manual. Or, look in the index. Next, check your manual for the car’s engine speed. Once you find those numbers, multiply them together. For instance, if the torque is 480 and the engine speed is 2,500 rotations per minute, multiply those together to get 1,200,000. Finally, divide the product by 5,252 to find the horsepower. In our example, 1,200,000/5,252 = 228.48. Round to the nearest whole number to get a horsepower of 228. To calculate the horsepower of an electric motor, you’ll use a slightly different formula. Look at the manufacturer’s information to find the voltage (V), current in amps (I), and efficiency (Eff) of the motor. Then, use the formula (V x I x Eff)/746 to find the horsepower. For example, a motor with a voltage of 240, a current of 100 amps, and an efficiency of 82%, or .82, would have a horsepower of (240 x 100 x .82)/746, or 26.38. For more tips, including how to calculate the horsepower of an electric motor or a human, keep reading!
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