Moment of Force Converter
What this converter does
A moment of force is the turning effect of a force about an axis. Wrench settings, motor data, beam calculations and older engineering drawings describe it in different units: N·m in modern SI documents, kN·m in structural work, kgf·m in legacy metric catalogues, and lbf·ft on American tools. This converter translates a known moment between those units. It does not calculate the moment from a force and a lever arm, and it does not recommend a tightening value.
How the conversion works
The moment is M = F × d, where F is the force and d is the perpendicular distance from the axis to the line of action. Every supported unit is a force unit multiplied by a length unit, so each has a fixed value in newton metres. The converter multiplies your input by the source value and divides by the target value:
| Unit | Value in N·m |
|---|---|
| kN·m | 1,000 |
| mN·m | 0.001 |
| µN·m | 0.000001 |
| kgf·m | 9.80665 |
| gf·cm | 0.0000980665 |
| lbf·ft | 1.3558179483 |
| tonf (short)·m | 8,896.4432305 |
| tonf (long)·m | 9,964.0164182 |
| tonf (metric)·m | 9,806.65 |
| pdl·ft | 0.0421401101 |
| pdl·in | 0.0035116758 |
The kilogram-force uses standard gravity, 9.80665 m/s², exactly. The pound-force is 0.45359237 kg × 9.80665 m/s² ≈ 4.448222 N, and the poundal is 1 lb·ft/s² ≈ 0.138255 N.
Worked example
A bicycle stem bolt is specified at 40 N·m, but the available click wrench reads in lbf·ft. Dividing 40 by 1.3558179 gives 29.50 lbf·ft. In the opposite direction, a US lug-nut value of 120 lbf·ft becomes 120 × 1.3558179 = 162.70 N·m.
Legacy units work the same way: a drawing that states 2.5 kgf·m equals 2.5 × 9.80665 = 24.52 N·m.
What the result means
The number after conversion is the same turning moment expressed in a different unit system. A torque of 1 kN·m is exactly 1,000 N·m, so a result that looks 1,000 times too large or small is a prefix error rather than a physics difference. Note that N·m for torque and the joule for energy share base units but are not interchangeable quantities; this page keeps the moment unit.
Accuracy and limitations
- Converted figures inherit the tolerance of the original specification. A tool rated ±4 % remains ±4 % after the unit changes.
- Tightening torque is only an indirect proxy for bolt tension; friction, lubrication and thread condition change the clamp load produced by the same torque.
- Short, long and metric ton-force differ by roughly 12 %, so confirm which one a document uses before converting.
- Always follow the manufacturer's value and procedure for safety-critical fasteners.
Sources
- BIPM SI Brochure — the newton metre and the distinction between moment of force and energy.
- NIST SP 811 Appendix B.9 — conversion factors grouped by physical quantity.
- NIST SP 811 Appendix B.8 — definitions of pound-force, kilogram-force and poundal.
Editorial record
Written and reviewed by the SoupCalc Editorial Team. Last reviewed: September 25, 2026.