Torque is a measure of rotational force that causes an object to rotate around an axis. It describes how strongly a force acts on an object to produce twisting or turning motion. In everyday terms, torque explains how easy or difficult it is to rotate something, such as turning a wrench, opening a door, or tightening a bolt.In physics and engineering, torque is often called the moment of force.
Torque Converter
Convert torque between N·m, lb·ft, kg·m, dyne·m, and other torque units with scientific precision.
⚠️ Important: Torque calculations are critical for mechanical design. This tool provides technical conversions only. Always verify units and consult engineering references for equipment specifications and design applications.
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What Is Torque?
Torque Definition
Torque is defined as the product of the applied force and the perpendicular distance from the axis of rotation: τ = F × r × sin(θ).
- τ (tau) = Torque
- F = Applied force
- r = Distance from the axis of rotation (lever arm)
- θ = Angle between the force and the lever arm
Torque Units Explained
Newton Meter (N·m)
The SI unit of torque (moment of force). It represents the rotational force applied at a distance. τ = F × r.
Common uses: International standards, engineering design, scientific research, mechanical specifications.
Pound-Force Foot (lbf·ft)
Torque in US customary units. 1 lbf·ft ≈ 1.356 N·m. Widely used in US mechanical engineering.
Common uses: US automotive, machinery specifications, HVAC equipment, aerospace.
Pound-Force Inch (lbf·in)
Torque in smaller US units. 1 lbf·in ≈ 0.113 N·m. Used for precision equipment and small motors.
Common uses: Electric motors, precision machinery, fastener specifications.
Kilogram-Force Meter (kgf·m)
Torque using kilogram-force units. 1 kgf·m ≈ 9.807 N·m. Used in some regions and older standards.
Note: Represents force equivalent to weight of 1 kilogram.
Torque Calculation
Torque is the product of force and perpendicular distance from the axis: τ = F × r × sin(θ)
- τ: Torque (N·m)
- F: Applied force (Newtons)
- r: Distance from axis of rotation (meters)
- θ: Angle between force and lever arm
Relationship between Torque and Power
Power is related to torque and rotational speed: P = τ × ω
- P: Power (Watts)
- τ: Torque (N·m)
- ω: Angular velocity (rad/s)
- Alternative: P = τ × N / 9549 (where N is rpm)
Typical Torque Values
- Hand torque (wrench): 10-50 N·m (7-37 lbf·ft)
- Car engine: 200-400 N·m (150-300 lbf·ft)
- Truck engine: 1000-2000 N·m (740-1480 lbf·ft)
- Small electric motor (1/4 hp): 0.5-2 N·m (4-15 lbf·in)
- Industrial motor (10 hp): 50-100 N·m (37-74 lbf·ft)
- Wheel tightening (car): 100-150 N·m (74-110 lbf·ft)
- Hydraulic systems: 10,000+ N·m (7,400+ lbf·ft)
Torque and Rotational Motion
Torque causes angular acceleration, analogous to force causing linear acceleration:
- Linear motion: F = m × a
- Rotational motion: τ = I × α
- Rotational kinetic energy: KE = ½ × I × ω²
- Angular momentum: L = I × ω
Torque in Equipment Specifications
Common torque specifications found in engineering:
- Motors: Starting torque, rated torque, peak torque
- Fasteners: Torque specifications for bolts and screws
- Transmissions: Maximum torque handling capability
- Bearings: Torque ratings under load
- Pumps: Minimum torque required to operate
- Compressors: Starting and running torque
Common Applications
Torque calculations are essential in:
- Mechanical Design: Motor selection, coupling sizing
- Fastening: Bolt torque specifications
- Automotive: Engine performance, wheel bearing, transmission
- Robotics: Joint motor sizing, load calculations
- Power Transmission: Shaft and gear design
- Heavy Machinery: Crane operation, lifting equipment
- Industrial Equipment: Pumps, compressors, fans