Hydraulic Motor Torque & Speed Calculator
Hydraulic Motor Torque & Speed Calculator
Estimate hydraulic motor speed, torque and output power from displacement, flow, pressure and efficiency.
Formula: n ≈ Q × 1000 ÷ Vg; M ≈ Δp × Vg ÷ (20π)
Use these results as engineering estimates. Always check the carrier, hydraulic circuit and attachment manufacturer specifications before selecting or operating equipment.
Estimate hydraulic motor speed, torque and power
Hydraulic motors convert oil flow and pressure into rotary motion. Flow primarily influences rotational speed, while pressure differential and motor displacement determine theoretical torque. Real output depends on volumetric and mechanical efficiency.
This calculator estimates motor rpm, torque and output power from motor displacement, flow, pressure differential and efficiency values. It is useful for first-pass comparisons of motor-driven attachments such as augers, sweepers, mulchers, cutters, conveyors and hydraulic rotators.
Displacement and motor speed
Motor displacement is commonly stated in cubic centimetres per revolution. A larger displacement motor uses more oil per revolution and therefore turns more slowly at the same flow. A smaller displacement can produce higher speed but generally less torque at the same pressure.
Pressure differential and torque
The useful torque of a hydraulic motor depends on the pressure difference between inlet and outlet. High return pressure reduces the effective pressure differential and therefore the torque available at the shaft. Case-drain requirements and maximum back pressure must be checked in the motor manufacturer’s documentation.
Do not size a motor from one number alone
A motor must be suitable for the required speed, continuous and peak pressure, duty cycle, oil viscosity, case pressure and expected shock loading. The attachment’s gearing or drive ratio can also significantly change final output speed and torque.
Use the Hydraulic Power Calculator to compare the overall power available from the circuit, and the Hose Flow Velocity Calculator when reviewing line size.
Frequently asked questions
Does more flow increase hydraulic motor torque?
Flow mainly increases motor speed. Torque is primarily related to displacement and pressure differential.
Does more pressure increase motor speed?
Not directly. Pressure is generated in response to load and is primarily related to available torque. Speed is primarily controlled by flow.
Why include volumetric and mechanical efficiency?
Internal leakage reduces actual speed, while friction reduces usable torque. Efficiency inputs provide a more realistic estimate than purely theoretical values.
How to use this calculator
Use this calculator for a first estimate of hydraulic motor speed and torque. It is relevant to rotators, augers, sweepers, mulchers and other attachments where motor displacement must be matched to available flow and pressure.
Typical uses
- Estimate motor rpm from displacement and available flow.
- Estimate output torque from motor displacement and pressure difference.
- Compare alternative motor sizes before checking manufacturer performance curves.
Frequently asked questions
What mainly controls hydraulic motor speed?
Flow and motor displacement are the main factors. Higher flow raises speed, while a larger displacement generally lowers speed for the same flow.
What mainly controls hydraulic motor torque?
Torque is primarily related to pressure difference and motor displacement, with mechanical efficiency reducing the real output.
Can this replace a motor manufacturer performance curve?
No. Real motors have leakage, starting torque limits, case-drain requirements and efficiency changes that must be checked in the manufacturer data.