Torque is the rotational equivalent of force. This guide explains what it is, how it's measured, and key applications.
What is Torque?
Torque (τ) is the tendency of a force to cause rotation: τ = r × F × sin(θ). SI unit: newton‑meter (N·m).
Key Concept
More force or a longer lever arm increases torque. That is why wrenches have long handles.
Units of Torque
SI Units
- Newton‑meter (N·m)
- Kilonewton‑meter (kN·m): 1000 N·m
- Millinewton‑meter (mN·m): 0.001 N·m
Other Units
- Pound‑foot (lb·ft): 1.3558 N·m
- Pound‑inch (lb·in): 0.11298 N·m
- Kilogram‑meter (kgf·m): 9.8067 N·m
Types of Torque
Static
No angular acceleration.
Ex: Tightening a bolt
Dynamic
Causes angular acceleration.
Ex: Engine accelerating
Reaction
Opposes another torque.
Ex: Helicopter tail rotor
Torsional
Twists an object.
Ex: Drive shaft
Torque Conversion Table
| Unit | N·m | lb·ft | lb·in | kgf·m |
|---|---|---|---|---|
| 1 N·m | 1 | 0.7376 | 8.8507 | 0.1020 |
| 1 lb·ft | 1.3558 | 1 | 12 | 0.1383 |
| 1 lb·in | 0.1130 | 0.0833 | 1 | 0.0115 |
| 1 kgf·m | 9.8067 | 7.2330 | 86.7962 | 1 |
Measuring Torque
Torque Wrench
Apply specific torque.
Auto/mechanics
Strain Gauge
Measure via strain.
Industrial
Optical Sensor
Measure twist optically.
R&D
Applications of Torque
Automotive
- Engine performance
- Wheel lug nuts
- Drivetrain
Manufacturing
- Assembly
- Robotic arms
- Conveyors
Aerospace
- Engines/propellers
- Control surfaces
- Landing gear
Medical
- Surgical tools
- Prosthetics
- Dental devices
Did You Know?
Bugatti Chiron: ~1,600 N·m. Wärtsilä‑Sulzer RTA96‑C: ~7,603,850 N·m (102 RPM).
Torque in Everyday Life
Common Values
- Bike pedal ~35–55 N·m
- Wheel nuts ~90–120 N·m
- Spark plug ~20–30 N·m
Human Torque
- Grip ~50 N·m
- Elbow flex ~75/45 N·m (m/f)
- Knee ext ~250/150 N·m (m/f)
Practical Tip:
Use a torque wrench; follow specs and correct units. For critical joints, consider torque‑angle.