Calculate the relationship between motor power, shaft torque, and rotational speed in common engineering units. The calculator can solve for any one of the three variables and account for transmission efficiency.
Power–Torque–Speed Calculator
Calculate power, torque, or rotational speed from the other two values. Values are converted to SI units before calculation.
Formula and calculation steps
Note: Results are for information and preliminary engineering only. Verify applicable standards, safety factors, and manufacturer data for critical decisions. Tool version 2.7.1
How are power, torque, and rotational speed related?
In a rotating system, mechanical power equals torque multiplied by angular speed. When any two values are known, the third can be calculated for preliminary motor, gearbox, and shaft sizing.
How to use the calculator
- Select whether you want to calculate power, torque, or rotational speed.
- Enter the two known values and select their engineering units.
- Enter the system efficiency if transmission losses must be included.
- Select Calculate to view the result, equation, and calculation summary.
Equations used
T = 9550 × P × η / n
P = T × n / (9550 × η)
n = 9550 × P × η / T
In these equations, P is power in kW, T is torque in N·m, n is speed in rpm, and η is efficiency as a decimal ratio. Supported units include W, kW, hp, PS, N·m, N·cm, kgf·m, lbf·ft, rpm, rad/s, and Hz.
How should the results be evaluated?
Use the result for preliminary design and verification. Critical applications also require manufacturer data, duty-cycle assessment, service factors, safety factors, and the applicable engineering standards.
Input guide for Power–Torque–Speed Calculator
Calculate power, torque, or rotational speed from the other two values. The table below summarises the inputs and example starting values.
| Parameter | Example value | Units and description |
|---|---|---|
| Value to calculate | Torque | Select power, torque, or speed. |
| Power | 15 | kW, W, hp, PS — Motor or shaft power. |
| Torque | 95.5 | N·m, N·cm, kgf·m, lbf·ft — Turning moment at the shaft. |
| Speed | 1500 | rpm, rad/s, Hz — Rotational speed. |
| Efficiency | 100 | % — Represents transmission losses. |
Example calculation scenario
For an initial check, enter the example values from the table, select the required units, and choose Calculate. Review the main result and equation, then replace the examples with measured or design data from your system.
Common mistakes when using Power–Torque–Speed Calculator
- Ignoring transmission efficiency, service factor, or transient operating conditions.
- Mixing unit systems without checking the selected units.
- Using example values instead of measured or design data from the actual system.
- Accepting the result without checking safety factors, duty cycle, and manufacturer limits.
Fundamental equation: T = 9550 × P × η / n
Frequently asked questions
What is a power, torque, and speed calculator used for?
It calculates the unknown power, torque, or rotational speed of a motor, gearbox, or rotating shaft when the other two values are known.
Where does the constant 9550 come from?
It comes from converting angular speed between revolutions per minute and radians per second while using kilowatts and newton metres in P = Tω.
How does efficiency affect the result?
An efficiency below 100 percent accounts for transmission losses and reduces the usable output power or torque.
