Electric Motor Torque Calculator

Calculate torque, power, and speed for any electric motor instantly.

Staring at a motor nameplate, trying to figure out how much torque it produces? You’re not alone. Motor specs often give you horsepower and RPM, but what about the torque value that actually matters for your application? Nowhere to be found.

This calculator solves that problem. Enter any two values — power, torque, or speed — and instantly get the third. Works with HP, kW, lb-ft, Nm, and RPM. No more hunting for formulas or converting between units manually.

Select what you want to calculate and get your answer in seconds.

Electric Motor Torque Calculator | Free HP to Torque & kW to Nm Calculator

🔄 Calculate Torque from Power & Speed

↻

Power (P) Speed (n) Torque (T)

✓ Known: Power ✓ Known: Speed ? Calculate: Torque

⚠️ Please enter valid values.

Motor Power (Rated Power)

Rotational Speed (Motor Speed)

📊 Torque Results

🔄 All Torque Units

⚡ Calculate Power from Torque & Speed

↻

Power (P) Speed (n) Torque (T)

✓ Known: Torque ✓ Known: Speed ? Calculate: Power

⚠️ Please enter valid values.

Torque (Motor Torque)

Rotational Speed (Motor Speed)

📊 Power Results

⚡ All Power Units

🔁 Calculate Speed from Power & Torque

↻

Power (P) Speed (n) Torque (T)

✓ Known: Power ✓ Known: Torque ? Calculate: Speed

⚠️ Please enter valid values.

Motor Power (Rated Power)

Torque (Motor Torque)

📊 Speed Results

🔁 All Speed Units

📖 How to Use This Calculator

Select Calculation

Choose whether to calculate torque, power, or speed

Enter Known Values

Input the two values you know with correct units

Click Calculate

Get instant results in multiple units

Use Results

Copy or use the calculated values for your application

⚙️ Understanding Motor Torque, Power & Speed

🔄 What is Torque?

Torque is the rotational force that the motor shaft can deliver. It determines how much “twisting power” is available to move a load.

Units: lb-ft, Nm, oz-in, kg-m

High torque motors are ideal for starting heavy loads, conveyors, and applications requiring strong initial force.

⚡ What is Power?

Power is the rate of doing work. It represents how quickly the motor can deliver energy to perform a task.

Units: HP (Horsepower), kW, Watts

Power = Torque × Speed. A motor can produce the same power with high torque/low speed OR low torque/high speed.

🔁 What is Speed?

Speed (RPM) indicates how fast the motor shaft rotates per minute. It’s determined by motor design and electrical frequency.

Units: RPM, RPS, rad/s

Common speeds: 3600, 1800, 1200, 900 RPM (synchronous) or slightly less under load.

📐 Motor Torque Formulas

Calculate Torque (Imperial)

T = (HP × 5252) ÷ RPM

Result in lb-ft. The constant 5252 = 33,000 ÷ (2π), where 33,000 is ft-lb/min per HP.

Calculate Torque (Metric)

T = (kW × 9549) ÷ RPM

Result in Nm. The constant 9549 = 60,000 ÷ (2π).

Calculate Power (Imperial)

HP = (T × RPM) ÷ 5252

Where T is in lb-ft. Use this when you know torque and speed.

Calculate Power (Metric)

kW = (T × RPM) ÷ 9549

Where T is in Nm. Converts rotational force to power output.

Calculate Speed

RPM = (HP × 5252) ÷ T

Or use kW version: RPM = (kW × 9549) ÷ T(Nm)

General Formula

P = T × ω

Where P = Power (Watts), T = Torque (Nm), ω = Angular velocity (rad/s)

📋 Common Electric Motor Ratings

Power (HP)	Power (kW)	@ 1800 RPM (lb-ft)	@ 1800 RPM (Nm)	@ 3600 RPM (lb-ft)
1/4	0.19	0.73	0.99	0.36
1/2	0.37	1.46	1.98	0.73
1	0.75	2.92	3.96	1.46
2	1.5	5.84	7.92	2.92
5	3.7	14.6	19.8	7.3
10	7.5	29.2	39.6	14.6
25	18.6	73	99	36.5
50	37.3	146	198	73
100	74.6	292	396	146

🔌 Electric Motor Types

🔄

AC Induction Motors

Most common industrial motor. Runs at near-synchronous speed (1750, 3500 RPM). Reliable and low maintenance.

⚡

Synchronous Motors

Runs exactly at synchronous speed. Used for precision applications and power factor correction.

🎯

DC Motors

Excellent speed control. High starting torque. Used in variable speed applications.

🔋

Brushless DC (BLDC)

High efficiency, low maintenance. Common in EVs, drones, and precision equipment.

🎚️

Servo Motors

Precise position control. High torque at low speeds. Used in robotics and CNC machines.

📏

Stepper Motors

Discrete step positioning. Open-loop control. Popular in 3D printers and automation.

🔄 Unit Conversion Reference

Horsepower

1 HP = 0.7457 kW = 745.7 W

Kilowatt

1 kW = 1.341 HP = 1000 W

lb-ft

Pound-foot

1 lb-ft = 1.356 Nm

Newton-meter

1 Nm = 0.7376 lb-ft

oz-in

Ounce-inch

1 oz-in = 0.00521 lb-ft

RPM

Revs per minute

1 RPM = 0.1047 rad/s

📈 Torque-Speed Relationship

🔗 The Power-Torque-Speed Triangle

Power, torque, and speed are interconnected. At constant power:

Higher speed = Lower torque
Lower speed = Higher torque

This is why gear reducers are used — they trade speed for increased torque.

⚙️ Using Gear Reducers

A gear reducer (gearbox) changes the torque-speed relationship:

10:1 ratio: Speed ÷ 10, Torque × 10
Allows small motors to drive heavy loads
Some efficiency loss (typically 2-5% per stage)

📊 Base Speed vs Field Weakening

DC and VFD-controlled motors have two operating regions:

Below base speed: Constant torque available
Above base speed: Constant power (torque decreases)

Important for applications requiring wide speed ranges.

❓ Frequently Asked Questions

How do I calculate motor torque from horsepower?

Use the formula: Torque (lb-ft) = (HP × 5252) ÷ RPM. For example, a 10 HP motor running at 1750 RPM produces: (10 × 5252) ÷ 1750 = 30 lb-ft of torque. The constant 5252 comes from unit conversions (33,000 ft-lb/min per HP ÷ 2π).

What’s the difference between starting torque and running torque?

Starting torque (locked rotor torque) is the torque produced when the motor first starts from standstill. Running torque (full load torque) is the torque at rated speed. Starting torque is typically 150-300% of running torque for induction motors, which helps overcome initial load inertia.

Why is 5252 used in the torque formula?

The constant 5252 comes from: 33,000 ft-lb/min (definition of 1 HP) ÷ 2π (radians per revolution). This converts between rotational mechanical power and the linear definition of horsepower. For metric calculations, use 9549 when working with kW and Nm.

How does motor speed relate to frequency?

For AC motors, synchronous speed = (120 × Frequency) ÷ Number of Poles. At 60 Hz: 2-pole = 3600 RPM, 4-pole = 1800 RPM, 6-pole = 1200 RPM. Actual running speed is slightly less due to “slip” (typically 2-5% for induction motors).

How do I convert lb-ft to Nm?

Multiply lb-ft by 1.3558 to get Nm. For example, 30 lb-ft × 1.3558 = 40.67 Nm. Conversely, multiply Nm by 0.7376 to get lb-ft. Our calculator does these conversions automatically.

What is a motor’s service factor?

Service factor (SF) indicates how much a motor can be overloaded continuously. A motor with SF 1.15 can handle 115% of rated load. This provides a safety margin for occasional overloads but running at service factor continuously reduces motor life.

Can I increase torque without changing the motor?

Yes, by using a gear reducer. A gearbox trades speed for torque — a 5:1 reduction increases torque by 5× while reducing speed by 5×. Belt/pulley systems and chain drives can also change the torque-speed ratio.

What’s the relationship between torque and current?

Motor torque is roughly proportional to current squared for induction motors. Higher load = higher current. This is why starting current is high (400-800% of full load) — the motor produces high starting torque to overcome inertia.

How do VFDs affect motor torque?

Variable Frequency Drives (VFDs) maintain constant torque from 0 Hz up to base frequency (usually 60 Hz) by keeping the V/Hz ratio constant. Above base frequency, voltage is limited, so torque decreases while power remains constant (field weakening region).

What’s the difference between peak torque and continuous torque?

Continuous torque is what the motor can sustain indefinitely without overheating. Peak torque is the maximum torque available for short periods (acceleration, starting). Peak torque is typically 2-4× continuous torque for servo motors and depends on thermal limits.