Calculate RPM from horsepower and torque, or solve for HP or torque, with HP, kW, lb-ft and N-m units plus a constant-power torque band and gearbox output.
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HP to RPM Formula
The following formula is used to calculate the rotational speed (RPM) for a given horsepower and torque.
Variables:
- RPM is the rotational speed in revolutions per minute
- HP is the mechanical shaft horsepower, measured at the same operating point as torque
- T is the torque in pound-feet
For mechanical hp and torque in lb-ft, multiply horsepower by 33,000 / (2ฯ) โ 5252.113122 and divide by torque. The displayed formula uses the rounded constant 5252. The calculator uses P = ฯฯ with full-precision unit factors. Kilogram-force metres (kgfยทm), not kilogram-metres of mass, are the corresponding gravitational torque unit.
| Horsepower (HP, mechanical) | Rotational Speed (RPM) |
|---|---|
| 10 | 263 |
| 20 | 525 |
| 25 | 657 |
| 30 | 788 |
| 40 | 1,050 |
| 50 | 1,313 |
| 60 | 1,576 |
| 75 | 1,970 |
| 100 | 2,626 |
| 125 | 3,283 |
| 150 | 3,939 |
| 175 | 4,596 |
| 200 | 5,252 |
| 250 | 6,565 |
| 300 | 7,878 |
| 350 | 9,191 |
| 400 | 10,504 |
| 450 | 11,817 |
| 500 | 13,130 |
| 600 | 15,756 |
| * Rounded to the nearest RPM. Assumes constant torque ฯ = 200 lb-ft and mechanical hp; use 33,000/(2ฯ) โ 5252.113122 for the full-precision constant. This comparison is not an engine torque curve. | |
What is HP to RPM?
The relationship between horsepower (HP), torque (T), and rotational speed (RPM) is a fundamental concept in mechanical engineering and automotive industries. Horsepower is a measure of the engine’s power output, torque is a measure of the engine’s rotational force, and RPM is the number of revolutions the engine makes per minute. Understanding this relationship helps in optimizing engine performance and efficiency.
How to Calculate HP to RPM?
The following steps outline how to calculate the rotational speed (RPM) from horsepower and torque.
- First, determine the horsepower (HP).
- Next, determine the torque (T) in pound-feet.
- Next, calculate the rotational speed (RPM) using the formula RPM = (HP * 5252) / T.
- Finally, calculate the RPM.
- After inserting the values and calculating the result, check your answer with the calculator above.
Example Problem :
Use the following variables as an example problem to test your knowledge.
Horsepower (HP) = 300
Torque (T) = 400 lb-ft. The calculated speed is approximately 3,939.085 RPM. Power and torque must refer to the same shaft operating point; neither power alone nor the constant-power comparison establishes an engineโs actual speed range.
