electric motor torque calculator

What Is Motor Torque and Why It Matters

Electric motor torque is the turning force available at the shaft. If speed tells you how fast the motor spins, torque tells you how hard it can twist. Both are essential when you size motors for pumps, conveyors, fans, machine tools, EV drivetrains, or robotic systems.

Many designs fail not because the motor lacks power at top speed, but because it cannot deliver enough torque at startup, low speed, or peak load moments. A reliable torque estimate helps you avoid stalling, overheating, and short motor life.

Core Formula Used in This Calculator

The calculator uses the standard relationship between power, torque, and angular speed:

T (N·m) = P (W) / ω (rad/s)

Where:

• T = torque in newton-meters (N·m)
• P = mechanical power in watts (W)
• ω = angular velocity in radians per second (rad/s)

If your speed is in RPM, a common shortcut is:

T (N·m) = 9550 × P (kW) / n (RPM)

For imperial output, this page also reports lb-ft using 1 N·m = 0.73756 lb-ft.

How to Use This Electric Motor Torque Calculator

1) Enter Motor Power

Input the motor power value and choose units: W, kW, or hp.

2) Enter Rotational Speed

Input shaft speed in RPM or rad/s. Most nameplates list RPM directly.

3) Optional: Apply Efficiency

If your power value is electrical input rather than shaft output, check the efficiency option and enter motor efficiency. The calculator converts electrical input power to estimated mechanical output before calculating torque.

4) Read Results

You’ll get torque in N·m and lb-ft, along with mechanical power used in the final calculation.

Example Calculation

Suppose you have a 2.2 kW motor running at 1450 RPM:

• P = 2.2 kW
• n = 1450 RPM
• T = 9550 × 2.2 / 1450 = 14.49 N·m (approx.)

If that 2.2 kW is actually electrical input and efficiency is 90%, mechanical power is 1.98 kW, and shaft torque drops accordingly.

Practical Motor Sizing Tips

Continuous vs Peak Torque

Always separate continuous duty requirements from short peak events. Many applications need brief overload capability for acceleration or breakaway friction.

Startup and Breakaway Loads

Static friction, loaded conveyors, and compressors can demand significantly more torque at startup than during steady operation. If startup torque is ignored, the motor may stall even if steady-state calculations look fine.

Gearboxes Change Torque and Speed

A gearbox reduces output speed and multiplies torque (minus losses). If your motor torque seems insufficient, a ratio change may solve the problem without changing motor size.

Service Factor and Thermal Margin

Choose margin for real-world operation: voltage variation, ambient heat, duty cycle, and shock loading. Continuous operation near limits can quickly increase winding temperature and reduce insulation life.

Common Mistakes to Avoid

• Using electrical input power as if it were shaft output without efficiency correction.
• Mixing RPM and rad/s formulas incorrectly.
• Ignoring gearbox efficiency and transmission losses.
• Sizing only for nominal load and forgetting transient peaks.
• Confusing torque units (N·m vs lb-ft).

Quick Reference: Unit Notes

• 1 kW = 1000 W
• 1 hp ≈ 745.7 W
• 1 N·m ≈ 0.73756 lb-ft
• ω (rad/s) = 2π × RPM / 60

Final Thoughts

This electric motor torque calculator is a fast way to estimate shaft torque from known power and speed. Use it early in concept design, then refine with real load profiles, efficiency curves, and manufacturer torque-speed data before final motor selection.