Formula Used
Synchronous RPM: 120 × frequency ÷ motor poles.
Running RPM: synchronous RPM × (1 − slip percent ÷ 100).
Gear ratio: driven teeth ÷ driver teeth.
Pulley ratio: driven diameter ÷ driver diameter.
Total ratio: stage 1 ratio × stage 2 ratio × stage 3 ratio.
Output RPM: motor RPM ÷ total ratio.
Motor torque: 9550 × motor power in kW ÷ motor RPM.
Output torque: motor torque × total ratio × efficiency.
Wheel speed: π × wheel diameter × output RPM ÷ 60.
Tangential force: output torque ÷ load radius.
How to Use This Calculator
Choose the ratio mode that matches your drive. Use teeth for gears and sprockets. Use diameters for pulleys. Use multi-stage mode when one reduction drives another reduction.
Enter motor RPM from the motor nameplate. When nameplate RPM is unknown, enter frequency, poles, and slip. Add torque or power. The calculator can estimate the missing value when enough data is present.
Enter efficiency, service factor, load torque, wheel diameter, and load radius when known. Press calculate. Review the result above the form. Use the CSV or PDF buttons to save the report.
Why Gear Ratio Matters
An electric motor often spins faster than the machine needs. A gearbox, chain drive, belt drive, or pulley set changes that speed. The same change also affects torque. A reduction ratio lowers output RPM and raises shaft torque. A speed increase raises RPM but lowers torque. This calculator joins both ideas in one practical report.
Use it for conveyors, mixers, robotics, winches, pumps, fans, and small vehicles. It helps compare gear teeth, pulley diameters, target RPM, motor torque, motor power, efficiency, wheel speed, and service load. The result is not only a final RPM. It also shows torque after losses, tangential force, design torque, travel speed, and load status.
Important Input Choices
Motor RPM can be entered directly. It can also be estimated from frequency, motor poles, and slip. Synchronous speed equals 120 times frequency divided by poles. Running speed then subtracts slip. Use nameplate speed when available, because real motors change speed under load.
For a gear or sprocket stage, divide driven teeth by driver teeth. For pulleys, divide driven diameter by driver diameter. A driven gear with more teeth gives reduction. A smaller driven pulley gives speed increase. Multiple stages multiply together, so small changes can create large output differences.
Reading the Result
Output RPM equals input RPM divided by the total ratio. Output torque equals motor torque multiplied by ratio and efficiency. Efficiency matters because bearings, gear mesh, belts, and chains waste power. Use a lower efficiency for rough, worn, or heavily loaded systems.
Design torque uses the service factor. A high service factor is useful for shock loads, stops, starts, and uneven material flow. If your required load torque is higher than available output torque, choose more reduction, a stronger motor, or a lighter duty cycle.
Practical Tips
Always check shaft limits, bearing ratings, belt speed, chain pitch, lubrication, and thermal rise. Very high ratios may need multiple stages. Very low output RPM can overheat some motors without forced cooling. Use the calculator for planning, then confirm final selections with manufacturer data and site conditions. Keep records for each trial. Compare ratios before buying parts. A small table of runs can reveal safer speed, smoother starts, and better energy use over time.
FAQs
What is gear ratio in a motor drive?
Gear ratio compares input speed to output speed. A 4:1 ratio means the motor turns four times for one output turn. It reduces speed and increases torque.
How do I calculate output RPM?
Divide motor RPM by the total ratio. For example, 1750 RPM with a 5:1 reduction gives 350 output RPM before any speed variation.
Does a bigger driven gear increase torque?
Yes. A bigger driven gear creates reduction. It lowers RPM and raises torque, minus efficiency losses from gears, bearings, belts, or chains.
What efficiency should I enter?
Use known manufacturer data when possible. For rough planning, use lower values for worn, misaligned, or loaded systems. Better bearings and proper lubrication improve efficiency.
Can this calculator handle pulley systems?
Yes. Choose pulley diameter mode. Enter driver and driven diameters using the same unit. The calculator divides driven diameter by driver diameter.
What is service factor?
Service factor is a design allowance for shocks, starts, stops, and duty severity. Higher service factor reduces usable torque for safer selection.
Why is my output torque marked insufficient?
The required load torque is higher than usable torque after efficiency and service factor. Increase reduction, use a larger motor, or reduce the load.
Should I use synchronous RPM or nameplate RPM?
Use nameplate RPM when available. It includes normal slip. Synchronous RPM is useful for estimates when only frequency and pole count are known.