Advanced Conversion Tool
Enter shaft power, speed, loss allowance, and sizing factors. The calculator returns running torque and adjusted design torque.
Formula Used
Imperial shortcut: Torque (lb·ft) = Horsepower × 5252 ÷ RPM
Metric method: Torque (N·m) = Power (W) ÷ Angular velocity (rad/s)
Design torque: Running torque × Service factor × Shock factor
The calculator first converts the selected power unit into watts. It converts shaft speed into radians per second. Then it applies efficiency and calculates torque. Design torque is shown after service and shock factors are applied.
How to Use This Calculator
- Enter the shaft power value from your motor, engine, or drive data.
- Select the matching power unit.
- Enter shaft speed and choose the correct speed unit.
- Add efficiency if losses occur before the useful shaft.
- Use service and shock factors for sizing checks.
- Select the output torque unit and press the calculate button.
Shaft Horsepower and Torque Basics
Shaft horsepower describes power available at a rotating shaft. It is the usable output after engine, motor, belt, gear, or coupling losses. Torque describes twisting force. Speed describes how fast that force turns. These three values are linked. When power stays constant, torque falls as speed rises. When speed falls, torque rises for the same power. This calculator helps you see that relationship clearly.
Why Torque Matters
Torque is central to drives, pumps, fans, conveyors, mixers, crushers, and machine tools. A motor may have enough horsepower, yet still fail if starting torque is too low. A shaft may carry normal torque, yet fatigue under shock loads. Couplings, keys, chains, belts, and gearboxes also need torque values. Horsepower alone is not enough for safe sizing. Torque gives the mechanical load that parts must resist.
Understanding Shaft Power
Input power is often rated at the motor nameplate or engine crankshaft. Shaft horsepower should represent delivered power at the useful shaft. Efficiency accounts for losses between the source and the load. For example, a belt drive, reducer, or hydraulic coupling can reduce delivered power. Entering efficiency makes the result more realistic. A lower efficiency gives lower running torque because less power reaches the shaft.
Speed and Units
Rotational speed is usually entered in revolutions per minute. Some tests use revolutions per second or radians per second. The calculator converts each speed unit into angular velocity. It also converts torque into pound feet, pound inches, newton meters, and kilogram force meters. This helps when you compare datasheets from different countries or industries.
Design Allowances
Real machines rarely run under perfect steady loads. Shock, starts, jams, vibration, and overloads increase demand. The service factor and shock factor multiply the running torque. The result is design torque. Use it when selecting couplings, reducers, shafts, or fasteners. Conservative factors can reduce failure risk. Extreme values should still be checked by a qualified engineer.
Practical Checks
A high torque result may mean the shaft speed is very low. A low torque result may mean the shaft speed is very high. Review the entered speed before changing equipment size. Also compare calculated torque with thermal limits, bearing loads, and duty cycle. Repeated starts can heat motors and reducers. Heavy inertia can demand more acceleration torque than steady operation needs.
Good Practice
Use measured shaft speed when possible. Use delivered power, not only rated input power. Check both continuous and starting conditions. Compare the design torque with rated torque from the component maker. Keep units consistent. Review safety margins when loads are critical, intermittent, or hazardous. The result is an estimate, but it is a strong starting point for drivetrain decisions. Record each input so later checks remain traceable. Recalculate after any pulley, gear, or speed change. Small changes in speed can create large torque changes, especially on low speed shafts and heavy industrial loads.
FAQs
What does shaft horsepower mean?
Shaft horsepower is usable power measured at a rotating shaft. It is usually lower than input power because belts, gears, couplings, pumps, and other parts create losses.
What is the basic horsepower to torque formula?
For mechanical horsepower and RPM, use torque in pound feet equals horsepower times 5252 divided by RPM. The calculator also uses a watt and angular velocity method for other units.
Why is RPM required?
Torque depends on both power and speed. The same power at low RPM gives higher torque. The same power at high RPM gives lower torque.
Can I use kilowatts instead of horsepower?
Yes. Select kilowatt as the power unit. The calculator converts power into watts, then calculates torque from angular velocity.
What efficiency value should I enter?
Use the estimated delivered efficiency between the power source and useful shaft. Enter 100 for no loss. Enter a lower value when belts, gears, or couplings reduce power.
What is service factor?
Service factor is a sizing allowance for duty severity. Higher values are often used for heavy starts, frequent cycling, vibration, or uncertain loading.
What is shock factor?
Shock factor allows extra torque for sudden impacts, jams, or irregular loads. It multiplies running torque along with service factor.
Which torque unit should I choose?
Use the unit required by your datasheet or design standard. Pound feet are common in imperial work. Newton meters are common in metric work.
Can this calculator size a shaft alone?
No. Torque is only one part of shaft sizing. You must also check bending, fatigue, keyways, material, speed, bearings, and safety rules.
Why is zero speed not allowed?
Torque from power needs angular velocity. At zero speed, the formula divides by zero. Starting torque should be checked from motor or engine curves.
Is the result exact?
The math is precise for the entered values. Real machine accuracy depends on measured power, speed, efficiency, load variation, and correct safety factors.