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Motor

Torque Unit Converter

Convert torque between Newton-metres, pound-feet, pound-inches, oz·in, kg·cm and dyne·cm — covers all motor datasheet units.

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Formula

1 N·m = 0.7376 lb·ft = 8.851 lb·in = 141.6 oz·in

How It Works

Torque is the rotational equivalent of linear force — it is the product of a force and the perpendicular distance (moment arm) from the pivot point. The SI unit is the newton-metre (N·m). Common engineering units include pound-foot (lb·ft), pound-inch (lb·in), kilogram-force-centimetre (kgf·cm), and ounce-inch (oz·in). Conversion factors are exact and scale linearly: 1 N·m = 0.7376 lb·ft = 8.8507 lb·in = 10.197 kgf·cm = 141.61 oz·in.

Worked Example

A servo datasheet lists stall torque as 55 oz·in. Convert to N·m and kgf·cm for use in a European datasheet comparison. Step 1 — oz·in to N·m: 1 oz·in = 0.007062 N·m 55 oz·in × 0.007062 = 0.3884 N·m Step 2 — N·m to kgf·cm: 1 N·m = 10.197 kgf·cm 0.3884 × 10.197 = 3.96 kgf·cm Step 3 — N·m to lb·in: 1 N·m = 8.8507 lb·in 0.3884 × 8.8507 = 3.44 lb·in Result: 55 oz·in ≈ 0.39 N·m ≈ 3.96 kgf·cm ≈ 3.44 lb·in. The servo is suitable for a 0.35 N·m design requirement with a small margin.

Practical Tips

  • ✓Always note whether a datasheet quotes peak/stall torque or continuous rated torque — they can differ by a factor of 5× for servo motors
  • ✓For quick field calculations: 1 N·m ≈ 10 kgf·cm and 1 lb·ft ≈ 1.36 N·m are close enough (< 2% error) for sanity checks
  • ✓When comparing motors across regions, standardise on N·m early in the design phase to avoid conversion errors in calculations

Common Mistakes

  • ✗Confusing kgf·cm with N·cm — kgf·cm is about 9.81× larger because 1 kgf = 9.81 N
  • ✗Mixing lb·ft and lb·in — 1 lb·ft = 12 lb·in; this factor-of-12 error is common when reading automotive vs. small-motor datasheets
  • ✗Treating torque and energy as interchangeable — both have units of N·m, but torque is a vector (cross product) while energy is a scalar

Frequently Asked Questions

Torque units proliferated from different engineering traditions: N·m from the SI metric system, lb·ft from US automotive, lb·in from US small-motor and fastener industries, kgf·cm from older European and Asian metric practice, and oz·in from US RC hobby and servo markets. Modern international standards favour N·m.
Dimensionally yes — both are kg·m²/s² — but they measure different quantities. A joule is energy (work done moving through a path), while an N·m of torque is a rotational force acting at a radius. Confusing them numerically (without angular displacement context) is a dimensional error.
Power (W) = Torque (N·m) × Angular velocity (rad/s). Convert RPM to rad/s by multiplying by π/30. For example, a motor producing 2 N·m at 3000 RPM delivers P = 2 × (3000 × π/30) = 2 × 314.2 = 628 W.

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