Use the calculator below in Basic, AC Motor, or DC Motor mode to calculate torque, power, speed, and common motor-specific torque estimates.

Electric Motor Torque Calculator

Enter any 2 values to calculate the third.

How This Motor Torque Calculator Works

This page supports three different calculation modes so the tool matches the way people actually work with motors. Basic mode solves the core relationship between power, speed, and torque. AC Motor mode uses the same mechanical relationship but adds full-load, starting, breakdown, and service-factor torque estimates. DC Motor mode solves torque from voltage, current, efficiency, and speed, with an optional stall torque and no-load speed estimate.

Basic Mode Formula

The core motor torque relationship is mechanical power equals torque multiplied by angular speed.

P = T × ω

For everyday motor sizing, the most common rearrangements are below.

  • T (N-m) = P (W) × 60 / (2Ï€ × RPM)
  • T (N-m) = 9550 × P (kW) / RPM
  • T (lb-ft) = 5252 × HP / RPM

AC Motor Mode

AC motor mode calculates the rated full-load torque from power and speed, then applies optional multipliers for common motor specification values.

  • Full-load torque comes from rated power and rated speed.
  • Starting torque = full-load torque × starting torque multiplier.
  • Breakdown torque = full-load torque × breakdown torque multiplier.
  • Service-factor torque = full-load torque × service factor.

DC Motor Mode

DC motor mode starts from electrical input and estimated mechanical output. It uses voltage, current, efficiency, speed, and torque to solve the missing value.

T = (V × I × η × 60) / (100 × RPM × 2π)

If stall torque and no-load speed are provided, the calculator also gives a simple linear DC motor torque-speed estimate.

T at speed = Tstall × (1 - RPM / no-load RPM)

When to Use Each Mode

  • Use Basic when you only need the direct relationship between power, speed, and torque.
  • Use AC Motor when you want rated torque plus starting, breakdown, or service-factor torque estimates.
  • Use DC Motor when your known values are voltage, current, efficiency, and speed, or when you want a simple torque-speed estimate from stall torque and no-load speed.

FAQ

Is AC motor torque calculated differently from DC motor torque?

The core shaft torque relationship is the same, but AC motors and DC motors are often sized with different known inputs. AC motor users usually start with horsepower or kilowatts and rated speed. DC motor users often start with voltage, current, efficiency, stall torque, or no-load speed.

What is full-load torque?

Full-load torque is the torque a motor produces at its rated power and rated operating speed. It is usually the baseline value used to estimate starting torque, breakdown torque, and service-factor torque on AC motors.

Can I calculate torque from horsepower and RPM?

Yes. That is one of the most common motor calculations. In imperial units, torque in lb-ft is horsepower multiplied by 5252 and then divided by RPM.