Units and SI factors
All units are referenced to the SI base N·m (Newton metre).
| Unit | Name | Factor to SI | 1 unit = ? SI |
|---|
Torque in engineering practice
Torque is a force applied about a pivot, and its SI unit is the newton metre (N·m). It governs how tightly a bolt is clamped, how much a motor can turn, and whether a coupling will slip. In North American workshops the same job is often specified in pound-force feet (lbf·ft) or, for small fasteners, pound-force inches (lbf·in). Legacy Asian specifications sometimes still print kilogram-force metres (kgf·m).
Where each unit shows up
- N·m — automotive torque wrenches, electric-motor ratings and general machine design.
- lbf·ft — US automotive lug nuts, engine bolts and hand tools.
- lbf·in — small fasteners in electronics, appliances and small engines.
- kgf·m — older Japanese and Korean engine and vehicle specifications.
- kN·m — large diesel engines, wind-turbine gearboxes and industrial couplings.
Conversion gotchas
A common confusion is that torque and energy share the same physical dimensions (N·m = J), yet they mean different things — a torque wrench stores no energy at rest. Keep the units distinct in your head. Also watch the multiplier: 1 lbf·ft = 12 lbf·in, but 1 lbf·ft ≈ 1.356 N·m. Two handy anchors: 1 N·m ≈ 0.7376 lbf·ft and 1 kgf·m = 9.80665 N·m exactly (standard gravity).