Torque Converter

How to convert torque units

Type a torque figure, choose the unit it is in, and choose the unit your wrench or datasheet uses. Newton meters, pound-feet, pound-inches and kilogram-force meters all update from a single entry.

The newton meter is the internal base and each factor is exact, so a pound-foot spec converted to N-m gives the full 12 significant figures, and you round to whatever the wrench scale allows.

• Check whether the spec is in lb-ft or lb-in, they differ by a factor of 12.
• Type the value in the Value box, for example 100.
• Pick the From unit, for example Pound-foot (lb-ft).
• Pick the To unit, for example Newton meter (N-m).
• Read the result and set the wrench, rounding to the nearest mark rather than the last digit.

lb-ft, ft-lb, lb-in: the naming is a genuine hazard

Pound-foot and foot-pound are written both ways in the wild and almost always mean the same thing, a torque of one pound-force applied at a one-foot lever arm. Strictly, physicists reserve the foot-pound for work and energy and the pound-foot for torque, but service manuals and wrench markings use them interchangeably, so treat lb-ft and ft-lb as identical when reading a spec.

The dangerous pair is lb-ft against lb-in, which differ by exactly twelve. A 25 lb-in electronics fastener is 2.825 N-m; a 25 lb-ft reading is 33.9 N-m, twelve times more, and enough to strip a small screw or crack a plastic boss. Inch-pound wrenches exist as a separate tool precisely because that factor is easy to miss.

• 1 lb-ft = 12 lb-in exactly.
• ft-lb and lb-ft in a service manual mean the same torque.
• kgf-m appears in older Japanese and European manuals: 1 kgf-m = 9.80665 N-m.

Setting a torque wrench from a converted figure

A converted torque is only as useful as the tool that applies it. A click-type wrench is typically accurate to within about four percent of the setting and only across the middle of its range, so a value read to twelve digits should be rounded to the nearest usable mark. A spec of 135.581794833 N-m becomes 135 N-m on the wrench, and nothing is lost by that.

Two things the converter cannot do for you matter more than the last decimal place: the tightening sequence and the condition of the thread. A dry, lubricated, or thread-locked fastener reaches a different clamping force at the same torque, and a manual that specifies a torque-plus-angle procedure cannot be satisfied by a torque figure alone.