Engine Horsepower Calculator
Calculate the horsepower of an engine using one of the three methods below. Learn more about how these methods work below.
Calculate Using Elapsed 1/4 Mile Time
Calculate Using 1/4 Mile Speed
Calculate Using RPM & Torque
Engine Horsepower Estimate:
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Joe is the creator of Inch Calculator and has over 20 years of experience in engineering and construction. He holds several degrees and certifications.
How to Calculate Engine Horsepower
Horsepower is a measure of the power output of an engine or motor. You can calculate the horsepower of an engine using several methods. Some common methods are the elapsed time method, the trap speed method, and by using the RPM and torque of the motor.
Calculate Horsepower with the Elapsed Time Method
The elapsed time method is a way of finding engine horsepower using the time it takes a vehicle to complete a quarter-mile or 400-meter run. Using the quarter-mile time and the vehicle weight it’s possible to estimate the horsepower of the vehicle.
Use the following horsepower formula for the elapsed time method:
horsepower = weight ÷ (time ÷ 5.825)3
The weight is the weight of the vehicle in pounds and the time is the quarter-mile time in seconds.
For example, let’s calculate horsepower for a vehicle weighing 3,750 pounds that completes the quarter-mile in 13 seconds.
horsepower = 3,750 ÷ (13 ÷ 5.825)3
horsepower = 3,750 ÷ 2.2323
horsepower = 3,750 ÷ 11.12
horsepower = 337.4 HP
Calculate Horsepower with the Trap Speed Method
The trap speed method is a way of estimating horsepower using the weight of the vehicle and speed in a quarter-mile or 400-meter run.
Use this formula for horsepower using the trap speed method:
horsepower = weight × (speed ÷ 234)3
The weight is the vehicle weight in pounds and the speed is the max speed in the quarter-mile in miles per hour.
For example, let’s calculate horsepower for a vehicle weighing 3,750 pounds with a quarter-mile speed of 100 mph.
horsepower = 3,750 × (100 ÷ 234)3
horsepower = 3,750 × 0.4273
horsepower = 3,750 × 0.078
horsepower = 292.67 HP
Calculate Horsepower with the RPM & Torque Method
It’s possible to calculate the horsepower of an engine using the RPM and torque of the motor. The vehicle documentation should include the torque and RPM of the motor; it is likely be published online as well.
Here is the formula for horsepower using the RPM and torque of the motor:
horsepower = (RPM × torque) ÷ 5,252
For example, For example, let’s find the horsepower for a motor with a speed of 5,600 RPM with 350 foot-pounds of torque.
horsepower = (5,600 × 350) ÷ 5,252
horsepower = 1,960,000 ÷ 5,252
horsepower = 373.19 HP
You might be interested in our horsepower conversion calculators or our carburetor size calculator.