Motor Gearbox Torque Calculator
Calculate gearbox output torque using motor power, speed, gearbox ratio, and efficiency. Instant results in Nm and lb-ft with worked engineering examples.
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Motor Gearbox Torque Calculator
Calculations are standard engineering estimates based on nominal ratios and gearbox mechanical efficiencies. Real values depend on service factors and operational variables.
💡 Actual gearbox output torque depends on gearbox type, service factor, efficiency losses, and operating conditions.
How to Use Motor Gearbox Torque Calculator
Determining the final shaft torque delivered by an industrial gear reducer configuration is straightforward. Sizing your electrical drives and mechanical couplings accurately prevents drive system damage and motor overloading. Follow these instructions to compute your gearbox output torque metrics:
- Enter motor power: Input the nominal rated mechanical power shown on the electric motor's nameplate.
- Select kW or HP: Choose the power rating system unit (kW or HP).
- Enter motor RPM: Input the rated high-speed rotor shaft speed in revolutions per minute (RPM).
- Enter gearbox ratio: Input the reducer mechanical speed reduction ratio (e.g., enter 20 for a 20:1 gearbox).
- Enter gearbox efficiency: Input the mechanical efficiency rating of the gear assembly (defaults to 95%).
- Click Calculate: Click the "Calculate Torque" button to compute the results.
- Review motor torque and gearbox output torque: Review the calculated motor base torque, multiplied gearbox output torque in both Metric (Nm) and Imperial (lb-ft) units, and the gearbox multiplication factor.
Practical Industrial Engineering Example
Consider an industrial conveyor system powered by a 15 kW electric motor running at 1460 RPM, connected to a helical inline gearbox with a 15:1 ratio and an efficiency of 94%. To design the conveyor head pulley drive shaft, engineers calculate the torque as follows:
- • Step 1: Motor base torque is computed using the power and RPM: (9550 × 15) / 1460 = 98.12 Nm.
- • Step 2: Gearbox output torque multiplies this base value by the ratio and accounts for efficiency losses: 98.12 Nm × 15 × 0.94 = 1,383.5 Nm.
- • Step 3: Convert metric output torque to imperial: 1,383.5 Nm × 0.7376 = 1,020.5 lb-ft.
- • Step 4: The effective torque multiplication factor is: 15 × 0.94 = 14.1.
How to Calculate Motor Gearbox Torque
Calculating the output torque of a motor gearbox involves finding the baseline torque generated by the motor shaft and then multiplying that force based on the speed reduction ratio and gearbox mechanical efficiency losses. Follow this step-by-step engineering calculation process:
Step 1 — Calculate Motor Torque (Nm)
Determine the electric motor's nominal rotational torque based on its rated mechanical power output and rotor speed in RPM. If your input power is in Horsepower (HP), it is first converted to Kilowatts (kW) using the multiplier 0.746.
Step 2 — Calculate Gearbox Output Torque (Nm)
Multiply the motor torque by the gear ratio, then multiply by the mechanical efficiency decimal to account for friction losses, seal drag, and oil churning.
Step 3 — Convert to Imperial Torque (lb-ft)
To obtain the output torque in imperial units (pound-feet), multiply the Metric Newton-meter torque value by the standard conversion constant (0.737562).
Verified Engineering Worked Example
Given Parameters:
- Motor Power: 7.5 kW
- Motor Speed: 1450 RPM
- Gear Ratio: 20:1 (20)
- Gearbox Efficiency: 95% (0.95 decimal)
Step 1 — Calculate Motor Torque
Motor Torque (Nm) = (9550 × 7.5) ÷ 1450 = 71625 ÷ 1450 = 49.4 Nm (49.39655 Nm)
Step 2 — Calculate Gearbox Output Torque
Output Torque (Nm) = 49.39655 × 20 × 0.95 = 49.39655 × 19 = 938.6 Nm (938.5345 Nm)
Step 3 — Convert Gearbox Output Torque to lb-ft
Output Torque (lb-ft) = 938.5345 × 0.737562 = 692.2 lb-ft
Final Verified Results
- Motor Base Shaft Torque: 49.4 Nm
- Gearbox Output Torque (Metric): 938.6 Nm
- Gearbox Output Torque (Imperial): 692.2 lb-ft
- Torque Multiplication Factor: 19.0
Motor Gearbox Torque Chart
This engineering reference chart shows the motor shaft baseline torque and gearbox output torque ratings across standard three-phase industrial motor power ratings. The values are calculated assuming a rated motor speed of 1450 RPM and a gearbox mechanical efficiency of 95%.
| Power (kW) | Motor Torque (Nm) | 5:1 Output Torque | 10:1 Output Torque | 20:1 Output Torque |
|---|---|---|---|---|
| 0.75 kW | 4.94 Nm | 23.46 Nm | 46.93 Nm | 93.85 Nm |
| 1.5 kW | 9.88 Nm | 46.93 Nm | 93.85 Nm | 187.71 Nm |
| 2.2 kW | 14.49 Nm | 68.83 Nm | 137.65 Nm | 275.30 Nm |
| 3.0 kW | 19.76 Nm | 93.85 Nm | 187.71 Nm | 375.41 Nm |
| 5.5 kW | 36.22 Nm | 172.06 Nm | 344.13 Nm | 688.26 Nm |
| 7.5 kW | 49.40 Nm | 234.63 Nm | 469.27 Nm | 938.53 Nm |
| 11.0 kW | 72.45 Nm | 344.13 Nm | 688.26 Nm | 1376.52 Nm |
| 15.0 kW | 98.79 Nm | 469.27 Nm | 938.53 Nm | 1877.07 Nm |
| 18.5 kW | 121.84 Nm | 578.76 Nm | 1157.53 Nm | 2315.05 Nm |
| 22.0 kW | 144.90 Nm | 688.26 Nm | 1376.52 Nm | 2753.03 Nm |
Note: All calculations assume a base speed of 1450 RPM and gearbox efficiency of 95%. Actual output torques in application environments will vary depending on mechanical wear, thermal factors, and lubrications.
Motor Gearbox Torque Calculator Frequently Asked Questions
Gearbox output torque is the rotational force produced at the output shaft of a gear reducer. It is the result of multiplying the motor's input torque by the gearbox ratio, adjusted for internal mechanical efficiency losses. In industrial machinery, it represents the actual working force available to drive loads like conveyors, mixers, or winches.
Gearbox output torque is calculated by first finding the electric motor's nominal torque using its rated power and speed. This motor torque is then multiplied by the gear reduction ratio and the gearbox's efficiency percentage (expressed as a decimal). The primary formula is: Output Torque = Motor Torque × Gear Ratio × (Efficiency ÷ 100).
Yes, a gearbox increases torque while simultaneously reducing the rotational speed of the shaft. Since mechanical power is the product of torque and angular speed, reducing the output speed by a specific gear ratio multiplies the output torque by that same factor, minus minor mechanical friction and efficiency losses within the gear stages.
A gear ratio is the ratio between the number of teeth on the driving gear (input shaft) and the driven gear (output shaft). It defines the proportional reduction in rotational speed and the corresponding multiplication of rotational torque. For example, a 20:1 gear ratio reduces speed by a factor of 20 while multiplying torque by up to 20 times.
Gearbox efficiency determines how much mechanical power is lost as heat due to gear mesh friction, oil churning, and bearing resistance. A lower efficiency directly reduces the final output torque. For instance, a gearbox with 90% efficiency will deliver 10% less output torque than an ideal, frictionless gearbox operating at the same speed ratio.
Yes, motor torque can be calculated directly from motor power and rotational speed (RPM). Using standard metric units, the formula is: Torque (Nm) = (9550 × Power in kW) ÷ Speed in RPM. For imperial units, the formula is: Torque (lb-ft) = (5252 × Power in HP) ÷ Speed in RPM. This baseline torque is then fed into the gearbox equation.
Motor torque is the raw rotational force generated at the electric motor's high-speed shaft. Gearbox torque, or output torque, is the final multiplied force produced after the motor's shaft speed is reduced through gear assemblies. Gearbox torque is significantly higher than motor torque, depending on the gear ratio and gear efficiency.
Output torque is the critical parameter for selecting and sizing drive systems in industrial automation. It determines whether a motor-gearbox combination has sufficient force to overcome static friction, accelerate heavy inertia loads, and sustain operations of equipment like heavy duty conveyor belts, vertical hoists, and industrial fans.