Formula Used
Hydraulic horsepower: HP = (PSI × GPM) / 1714
Shaft horsepower: Shaft HP = Hydraulic HP × volumetric efficiency × mechanical efficiency
Motor speed: RPM = (GPM × 231 × volumetric efficiency) / displacement in³ per revolution
Motor torque: Torque lb-ft = (PSI × displacement × mechanical efficiency) / (2π × 12)
Torque horsepower: HP = (Torque lb-ft × RPM) / 5252
Electrical sizing estimate: Input HP = (Hydraulic HP / drive efficiency) × service factor
How to Use This Calculator
Select the mode that matches your known data. Use pressure and flow when pump delivery is known. Use displacement and speed when motor size and speed are known. Use torque and speed when the shaft load is known.
Enter efficiency values from motor data, tests, or safe estimates. Add a service factor for reserve capacity. Press calculate. Review shaft output, electric input, torque, flow, pressure, and yearly energy values. Export the result for maintenance records.
Example Data Table
| Pressure |
Flow |
Vol. Eff. |
Mech. Eff. |
Hydraulic HP |
Shaft HP |
| 1500 PSI |
12 GPM |
90% |
85% |
10.502 |
8.034 |
| 2500 PSI |
18 GPM |
92% |
88% |
26.254 |
21.247 |
| 3000 PSI |
25 GPM |
93% |
90% |
43.757 |
36.626 |
Hydraulic Motor Horsepower Guide
Why Horsepower Matters
Hydraulic motors convert pressurized oil into rotary motion. Horsepower shows how much useful work the shaft can deliver. A correct value helps engineers choose couplings, gearboxes, wiring, starters, and protection devices. It also helps maintenance teams compare actual machine behavior with expected performance.
The main inputs are pressure and flow. Pressure creates torque. Flow creates speed. Efficiency connects ideal fluid power with real shaft output. A motor with leakage, friction, or heat loss will produce less power than the theoretical number. That is why this calculator includes volumetric efficiency, mechanical efficiency, and drive efficiency.
Useful Sizing Checks
Start with the highest continuous load, not only a short peak. Enter the pressure available at the motor ports. Then enter the flow reaching the motor. If displacement and speed are known, use that mode to estimate required flow. If torque and speed are known, use that mode to check the horsepower demand directly.
The service factor is important for electrical planning. It gives reserve capacity for starting load, pressure spikes, cold oil, and duty cycle changes. A small reserve can reduce nuisance trips and overheating. A very large reserve can waste money and space. Review the calculated kilowatts before selecting a motor starter or drive.
Accuracy Tips
Use measured values when possible. Gauge pressure should be read close to the hydraulic motor. Flow should represent working flow, not pump nameplate flow. Oil temperature changes leakage and viscosity. Worn motors can lose efficiency. Filters, hoses, valves, and fittings can also lower available pressure.
Use the result as an engineering estimate. Final selection should also check manufacturer curves, allowable case pressure, minimum speed, maximum speed, and thermal limits. For mobile equipment, verify duty cycle and cooling capacity. For industrial systems, compare calculated power with breaker size and cable capacity.
A balanced design also protects seals and bearings. Excess pressure raises heat and stress. Low flow limits speed. Clean oil and stable temperature help the motor keep predictable torque during long shifts daily.
Good records make troubleshooting easier. Export the result after every sizing check. Save pressure, flow, efficiency, and output power with the machine file. Later, the same numbers can reveal wear, restriction, or changed operating conditions.
FAQs
1. What does hydraulic motor horsepower mean?
It means the power a hydraulic motor can deliver at its shaft. It depends on pressure, flow, speed, torque, and efficiency. It is lower than ideal hydraulic power because real motors have losses.
2. Which mode should I choose?
Choose pressure and flow when hydraulic supply data is known. Choose displacement and speed when motor size is known. Choose torque and speed when the driven load requirement is known.
3. Why is efficiency included?
Efficiency accounts for leakage, friction, heat, and drive losses. A motor rarely converts all fluid power into useful shaft output. Better efficiency gives more usable horsepower.
4. What is the 1714 constant?
The 1714 constant converts PSI and GPM into horsepower. It comes from standard hydraulic power unit conversions. It is used for U.S. customary hydraulic calculations.
5. Can this calculate electric motor size?
Yes. It estimates electric input horsepower using hydraulic horsepower, drive efficiency, and service factor. Final selection should also follow local codes and manufacturer data.
6. What service factor should I use?
Many designs use a value above 1.0 for reserve capacity. Heavy starts, shock loads, cold oil, and long duty cycles may need more allowance. Check your equipment standard.
7. Why does oil temperature matter?
Oil temperature changes viscosity and leakage. Hot oil can reduce efficiency. Cold oil can raise pressure and starting load. Both conditions can change actual horsepower demand.
8. Is this result final for design approval?
No. Treat it as an engineering estimate. Confirm results with motor curves, pressure ratings, speed limits, thermal capacity, wiring size, breaker size, and safety requirements.