ENGINEERING CALCULATOR
Free Motor Torque Calculator
Every electric motor converts electrical power into mechanical torque at a specific speed. The relationship is direct: torque equals power divided by rotational speed, modified by the motor’s efficiency. Whether you are sizing a stepper for a CNC axis, a servo for a robot joint, or an AC induction motor for a conveyor, the starting point is always the same — how much torque at what RPM.
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Free Online Tool
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Formula-Based Results
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Engineering Applications
Motor Torque Calculator
Enter power and RPM to calculate torque, or torque and RPM to calculate power.
T = P × 9.549 / n
Torque
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Power
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Efficiency-Adjusted Input
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Formula
T = (P × 9550) / (RPM × η)
ONLINE ENGINEERING TOOL
Motor Torque Calculator
Calculate motor torque, horsepower, and power output using motor speed, mechanical power, or torque input values.
Torque Output
27.29 N·m
Power Output
5.00 kW
Conversion Result
50.00 HP
Formula Used
T = P × 9.549 ÷ n
HOW IT WORKS
Motor Torque Formula — Power, Speed & the 5252 Constant
The formula that every motor torque calculator implements is a rearrangement of the power-torque-speed relationship from Machinery's Handbook and standardized in NEMA MG 1. Power equals torque times angular velocity — and from that single equation, every motor torque calculation follows.
Metric (SI) — T = P × 9.549 / n
T = P × 9.549 / n
T = torque (N·m)
P = power (W)
n = speed (RPM)
9.549 = 60/(2π)
Imperial — HP = T × RPM / 5252
HP = T × RPM / 5252
HP = horsepower
T = torque (lb·ft)
RPM = speed
5252 = 33000/(2π)
Worked Example: 7.5 kW Motor at 1,450 RPM
A 7.5 kW motor at 1,450 RPM produces T = 7.5 × 9,549 / 1,450 = 49.4 N·m of torque. In imperial units, this is equivalent to 36.4 lb·ft. At 1,450 RPM, the HP output is 10.0 HP (7.5 kW). If the motor is 88% efficient, the electrical input is 8.52 kW.
49.4
N·m torque
=
36.4
lb·ft torque
at
1450
RPM
Mechanical Output
7.5 kW / 10.0 HP
Torque (N·m)
49.4 N·m
Efficiency Input
88% → 8.52 kW
The Three Key Concepts
01
Metric — T = P × 9.549 / n
Power in watts (or kW), torque in N·m. For kW: T = P_kW × 9,549 / n. 9.549 converts RPM to rad/s. Efficiency must be accounted for when using electrical input power.
P_mech = P_elec × η02
Imperial — HP = T × RPM / 5252
Torque in lb·ft, power in HP. 5252 = 33000/(2π) — the conversion from linear work to rotational work. Output is shaft horsepower, not electrical input.
HP_mech = T × RPM / 525203
5,252 RPM Crossing Point
At 5,252 RPM, torque (lb·ft) and HP are numerically equal. Below 5,252 RPM, torque > HP. Above 5,252 RPM, HP > torque. In metric, crossing occurs at 9,549 RPM.
At 5252 RPM: HP = TWhat the Results Mean
Shaft Torque vs. Electrical Input
Torque calculations from electrical input power must account for motor efficiency (η). A 90% efficient motor requires 11% more electrical power than the mechanical output. Use the efficiency slider in the calculator above.
5,252 RPM Sanity Check
On any imperial dyno chart, torque and HP always cross at 5,252 RPM. If they do not, one axis is scaled differently. This is the fastest check for motor torque calculations.
Metric vs. Imperial
Metric crossing is at 9,549 RPM (kW and N·m). Since most industrial motors run below 3,600 RPM, the metric cross-over is rarely seen on data sheets. Use the appropriate formula for your unit system.
MOTOR EFFICIENCY DATA
Typical Motor Efficiencies by Type
The efficiency value you enter in a motor torque calculator changes the relationship between electrical input power and mechanical shaft power, as defined in IEEE 112 (the standard test procedure for electric motors). Higher efficiency means more of what you pay the utility for reaches the load.
Efficiency ranges, peak efficiency regions, and key loss factors for common motor types. Use these values as defaults when sizing motors and calculating torque from electrical input.
AC Induction Motors
Industry workhorses — efficiency varies with size and load. Premium efficiency (IE3/IE4) pays back rapidly.
| Size Range | Efficiency Range | Peak Region |
|---|---|---|
| 1–10 HP | 82–90% | 75–100% load |
| 10–200 HP | 90–95% | 75–100% load |
| Efficiency drops below 50% load — oversizing hurts | ||
DC & BLDC / Servo
DC brushed motors are simple and cost-effective. BLDC/servo motors offer higher efficiency across a broad speed range.
| Motor Type | Efficiency Range | Peak Region |
|---|---|---|
| DC Brushed | 70–85% | 50–80% load |
| BLDC / Servo | 85–95% | 20–100% load |
| BLDC: permanent magnet excitation eliminates rotor losses | ||
Stepper & Universal
Steppers are not rated as motor-only efficiency — system efficiency (motor + drive) is 50–70%. Universal motors are common in power tools.
| Motor Type | Efficiency Range | Peak Region |
|---|---|---|
| Stepper | 50–70% (system) |
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| Universal | 50–70% | Near max RPM |
| Steppers draw full current even when stationary — efficiency is not the design metric | ||
Motor Torque Questions
Frequently Asked Questions
Motor torque is the rotational force a motor produces at its output shaft, measured in newton-metres (N·m), pound-feet (lb-ft), ounce-inches (oz-in), or kilogram-centimetres (kg-cm). Torque is calculated from power and speed using T = P × 9.549 / n (metric) or T = HP × 5252 / RPM (imperial), where P is mechanical output power and n is rotational speed in RPM. A motor torque calculator performs this conversion automatically and accounts for motor efficiency, which relates electrical input power to mechanical shaft power.
Torque is the twisting force at the motor shaft — the ability to do work at a given instant. Horsepower is torque × RPM ÷ 5252 — the rate at which that work is done over time. A high-torque, low-RPM motor (truck diesel) and a low-torque, high-RPM motor (motorcycle engine) can produce the same horsepower. In electric motors, torque determines what load you can start and accelerate; power determines what speed you can maintain that load at.
This is a consequence of unit definitions, not physics. One horsepower is 33,000 foot-pounds of work per minute. Rotational power equals torque × angular velocity = T × RPM × 2π. Setting these equal gives HP = T × RPM × 2π / 33,000 = T × RPM / 5,252. At 5,252 RPM, the numerator and denominator cancel and HP = T (numerically). Below 5,252 RPM, torque (lb-ft) always exceeds horsepower. Above 5,252 RPM, horsepower always exceeds torque. If a dyno chart shows torque and HP crossing at any other RPM, the axes are scaled differently.
If you have the motor data sheet, use its rated efficiency at the expected operating point. If you do not yet have a specific motor selected, use these conservative defaults: AC induction 88%, DC brushed 78%, BLDC/servo 90%, stepper (system with drive) 65%, universal 60%. Motor efficiency peaks near 75–100% of rated load and drops significantly below 50% load — oversizing a motor hurts both capital cost and operating efficiency. For premium efficiency IE3/IE4 AC induction motors above 10 HP, use 92–95%.
1 N·m = 0.7376 lb-ft = 141.6 oz-in = 10.197 kg-cm. 1 lb-ft = 1.3558 N·m = 192 oz-in. 1 oz-in = 0.00706 N·m = 0.00521 lb-ft. 1 kg-cm = 0.09807 N·m. This motor torque calculator outputs torque in all four units simultaneously — no manual conversion needed. An electric motor torque calculator that does unit conversion for you removes one of the most common sources of motor sizing errors.
PRECISION MANUFACTURING SUPPORT
From Motor Torque to Machined Motor Components
You have calculated your motor torque. You know the frame size, shaft diameter, mounting face dimensions, and the torque and speed at the output shaft. The motor will bolt to a mounting plate, couple to a shaft with a rigid or flexible coupling, and drive a load through a pulley, gearbox, or leadscrew.
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