Torque Conversion: N·m, lbf·ft and lbf·in

Convert through newton-metres

To convert 100 N·m into pound-force feet, divide by approximately 1.355817948. The result is about 73.7562 lbf·ft. To convert back, multiply the unrounded result by the same factor. An alternative destination is pound-force inches: dividing 100 by approximately 0.112984829 gives about 885.0746 lbf·in. The latter numerical value is twelve times the pound-force-foot value because one foot contains twelve inches. Keep the entire destination unit attached to the result rather than shortening both to an ambiguous “pounds.”

Use a simple physical check

An illustrative perpendicular force of 50 N acting 0.2 m from an axis gives 50 × 0.2 = 10 N·m of torque magnitude. Doubling the perpendicular distance while keeping the force the same doubles the torque. Applying the same force directly through the axis gives zero moment arm and therefore zero torque about that axis. These relationships check the physical calculation before any unit conversion. A torque converter cannot establish that the force was perpendicular or that the quoted length is the correct moment arm.

Handle a source in pound-inches

A value of 120 lbf·in equals 10 lbf·ft because 120/12 = 10. Converting that result gives approximately 13.55818 N·m. Treating 120 lbf·in as 120 lbf·ft would instead produce approximately 162.6982 N·m, twelve times the intended value. This is a unit-label error, not a rounding difference. When copying a value from a specification or tool scale, write whether the length unit is inches or feet before entering the number. A familiar-looking value is not enough to identify the unit.

Separate torque from rotational power

Rotational power is related to torque and angular speed: P = torque × angular speed when angular speed is in radians per second. A torque value alone therefore does not determine horsepower or watts. A shaft can exert torque while stationary, and the instantaneous mechanical power associated with rotation is then zero. If the question asks for power, obtain the speed and use the appropriate model before converting power units. Do not apply a torque conversion factor to a horsepower rating simply because both describe a rotating machine.

Torque includes force and lever arm

For a force applied at an angle to a lever arm, the torque magnitude is force × lever-arm length × sine of the angle between them. With a perpendicular force, the sine factor is one. The SI unit is newton-metre, N·m. Torque and work can share force-times-distance dimensions, but describe different quantities; retain the torque label rather than rewriting a torque specification in joules. A unit conversion assumes the torque value has already been determined and does not infer the applied force, lever arm or tightening procedure.

Use force-based inch and foot factors

One pound-force foot equals approximately 1.355817948 N·m. One pound-force inch is one twelfth of a pound-force foot, approximately 0.112984829 N·m. A kilogram-force centimetre equals 0.0980665 N·m under standard gravity. Labels such as lb·ft and kg·cm on a torque converter refer to force-based units in this context, not a mass multiplied by a length. Preserve the full unit name when there is a risk of confusion. Mixing pound-inches with pound-feet creates a twelvefold error, even though both labels contain the word pound.

Preserve the specification beyond the number

The linked torque converter accepts a value and From and To unit choices. It does not supply a tightening specification, a fastener grade, a sequence, lubrication conditions or an angle-turn procedure. Those details can be essential to the source instruction and do not disappear when units are changed. Keep the original specified value and unit alongside the conversion. Round to a precision suitable for the specified tool and procedure rather than treating all calculator digits as a more precise engineering requirement than the source provides.

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