Torque Converter

Converts torque values between newton-meters (N·m), foot-pounds (ft·lb), inch-pounds (in·lb), and kilogram-force meters (kgf·m). The reference relationship is 1 N·m ≈ 0.7376 ft·lb. Conversion factors are exact to the precision of the published 1959 international yard and pound agreement.

Application contexts include automotive specifications (ft·lb in US service manuals, N·m in European), bicycle component torques (typically N·m), and machining work (in·lb for small fasteners).

The unit relationships derive from the definitions of force and length. One newton-meter equals a force of one newton applied perpendicular to a lever arm one meter long. Converting requires the conversions for both force (1 lbf = 4.4482 N) and length (1 ft = 0.3048 m), yielding the 0.7376 factor. Inch-pounds add a 12× factor relative to foot-pounds because of the inch-to-foot relationship. Kilogram-force meters use the standard gravity value (9.80665 m/s²) to convert mass-weight to newtons.

A worked example: a Toyota cylinder head bolt specified at 65 N·m converts to 47.9 ft·lb or 575 in·lb. A bicycle stem bolt specified at 5 N·m converts to 3.7 ft·lb or 44.3 in·lb. The latter is a useful illustration of why bicycle mechanics use N·m almost exclusively: the inch-pound figure is awkward and the foot-pound figure is too small for clean reading.

Application precision varies by context. Critical fasteners (head bolts, suspension components, axle nuts) require accurate torque to avoid failure modes ranging from leaks to wheel separation. Less critical fasteners (interior trim, valve covers) tolerate ±15% without consequence. The order of magnitude difference between an eyeglass screw (a few in·lb) and a wheel lug nut (~100 ft·lb) spans four orders of magnitude in torque, motivating the multiple unit conventions.

Limitations: torque measurement assumes a static lever arm at right angles to the applied force. Dynamic torque measurement (running shafts, impact tools) produces different values that the simple conversion does not address. Impact wrenches deliver short pulses at peak torques far above the wrench's nominal rating. Torque-to-yield bolts (used in modern engines) tighten by angle rather than torque past a baseline value, and the converter does not handle those specifications.