Torque Unit Converter: lbf-ft, N-m, kgf-m, and Inch-Pounds

Conversion
–
lbf-ft
–
N-m
–
kgf-m
–
in-lb
–
kN-m

Torque Conversion Result

Generated by calculatgeek.com Torque Unit Converter

Torque units and why the rig floor cares

Torque is the simplest quantity on this list conceptually, just a force multiplied by the length of the lever arm it acts through, yet it manages to show up in more unit systems than almost anything else on a drilling rig. Tong line pull gets measured in pounds, makeup torque charts arrive in lbf-ft, European top drive specs quote kN-m, older metric equipment is stamped in kgf-m, and small accessory fittings use inch-pounds. The converter above moves between all five without the mental gymnastics.

Diagram of torque as force times lever arm on a wrench turning a bolt, with 1000 lbf-ft shown as 1355.82 newton meters, 138.25 kilogram-force meters, and 12000 inch-pounds
Torque is force applied at the end of a lever arm. The same 1,000 lbf-ft of makeup torque expressed in four unit systems.

The stakes are real. Drill pipe connections have a specified makeup torque window published by the manufacturer, typically through API RP 7G, and both directions of error hurt. Under-torqued connections can wobble, leak, and eventually wash out or back off downhole. Over-torqued connections yield the shoulder, damage the threads, and can be nearly impossible to break out on the next trip. A crew reading a kN-m chart against a gauge calibrated in lbf-ft is one misplaced decimal away from either outcome.

The conversion factors

Everything runs through the newton meter, the SI unit. One pound-force foot is exactly 1.3558179 N-m, which follows from the definition of the pound-force (4.4482216 N) times the foot (0.3048 m). One kilogram-force meter is exactly 9.80665 N-m, standard gravity acting on one kilogram at the end of a one meter arm. Inch-pounds are simply lbf-ft divided by twelve.

  • 1 lbf-ft = 1.35582 N-m = 0.13826 kgf-m = 12 in-lb
  • 1 N-m = 0.73756 lbf-ft = 0.10197 kgf-m = 8.8507 in-lb
  • 1 kgf-m = 9.80665 N-m = 7.2330 lbf-ft
  • 1 kN-m = 1,000 N-m = 737.56 lbf-ft

A note on torque versus energy

A newton meter of torque and a joule of energy have identical base units, and this occasionally tempts people into treating them as interchangeable. They are not. Torque is a rotational force that may do no work at all if nothing rotates, while a joule is energy actually transferred. The distinction matters when you calculate rotary power at the bit: power equals torque times angular speed, so a top drive holding 30 kN-m at zero RPM delivers exactly zero horsepower, no matter how impressive the gauge looks.

One last practical habit: when a torque spec seems wildly off, check whether someone has confused lbf-ft with in-lb. The factor of twelve is the most common torque transcription error in the field, and it is large enough to be dangerous but small enough to look almost plausible on a gauge.

Related Calculators and Reference