What is Torque?
Torque is a rotational force — the tendency of a force to rotate an object about an axis. It equals force multiplied by the perpendicular distance from the axis (the lever arm).
Core Formula
τ = F × r
τ = torque (N·m or ft·lb)
F = force (N or lbf)
r = lever arm distance (m or ft)Torque Conversions
1 N·m = 0.7376 ft·lb = 8.8507 in·lb
1 ft·lb = 1.3558 N·m = 12 in·lb
1 in·lb = 0.1130 N·m = 0.0833 ft·lb
Example: 100 N·m bolt spec → 73.76 ft·lbPractical Examples
Wheel lug nut (100 N·m):
F on wrench = τ ÷ r = 100 ÷ 0.3 m = 333 N (≈75 lbf)
Engine peak torque (350 ft·lb):
= 350 × 1.3558 = 474.5 N·mCommon Torque Specs
- M6 bolt (steel): 10 N·m | M8: 25 N·m | M10: 50 N·m
- Bicycle pedal: 25-30 N·m
- Car wheel nuts: 100-130 N·m
- Cylinder head bolts: 60-120 N·m (engine-specific)
Convert torque units: Free Torque Calculator
Common Torque Values
- M6 bolt (8.8 grade): ~10 N·m tightening torque
- Car wheel nut (typical): 90–130 N·m
- Car engine (1.0L): ~100–150 N·m peak torque
- Car engine (V8): 400–700 N·m peak torque
- Bicycle crank bolt: 35–50 N·m
Torque in Mechanical Design
Torque (T = F × r) is the rotational equivalent of force. In engineering, it determines how tightly fasteners must be tightened (to achieve correct clamp force and avoid joint failure), the size of motors and gearboxes needed to drive machinery, and structural adequacy of shafts under torsional load. Undertightening bolts causes loosening under vibration and joint separation; overtightening causes thread stripping or bolt fracture. Correct torque is safety-critical in automotive, aerospace, and structural applications — hence the requirement for calibrated torque wrenches on safety-critical joints.
Frequently Asked Questions
What is the difference between torque and moment?
In engineering, torque typically refers to a twisting force about an axis of rotation (as in a shaft or bolt), while moment (bending moment) refers to a force causing rotation about a point in a structural context. Mathematically both are F × perpendicular distance, but the engineering contexts differ: torque relates to power transmission, moments to structural bending.
How does torque relate to power?
Power (W) = Torque (N·m) × Angular velocity (rad/s). In practical terms: Power (kW) = Torque (N·m) × RPM / 9549. This is why diesel engines with high torque at low RPM produce strong pulling power without high revs, while sports petrol engines achieve high power by combining moderate torque with very high RPM.
Why do engineers use different torque units?
SI units use Newton-metres (N·m). US engineering often uses pound-feet (lb·ft) or pound-inches (lb·in). 1 N·m = 0.7376 lb·ft. Automotive specifications frequently mix: engine torque in lb·ft (US) vs N·m (EU). Small fastener torques may be in N·cm or inch-pounds to avoid decimals.