Newton-Meter Converter — N·m, ft-lb and in-lb

Background.

Torque is the turning effect of a force about an axis. Its SI unit is the newton-metre, written N·m, but vehicle, bicycle, aviation and fastener documents often use pound-force feet or pound-force inches. Laboratory and older engineering sources may use kilogram-force metres or dyne-centimetres. This converter puts those units on one exact scale.

The “force” word matters. A pound-force is not a pound of mass; it is the force produced when the exact international pound is acted on by standard gravity. Using 0.45359237 kilograms per pound and 9.80665 metres per second squared gives exactly 4.4482216152605 newtons per pound-force. Multiplying by the exact international foot, 0.3048 metre, gives 1.3558179483314004 newton-metres per pound-force foot.

A pound-force inch is one twelfth of a pound-force foot because twelve inches make one foot exactly. That means 12 lbf·in equals 1 lbf·ft without approximation. It is easy to miss that factor when a specification abbreviates both as “lb” or “in-lb.” The selectors spell out force and distance so a mass or energy unit is not silently substituted.

Kilogram-force is another gravitational force unit. One kilogram-force is defined using standard gravity, so 1 kgf·m is exactly 9.80665 N·m. The dyne is the CGS force unit: one dyne is 10⁻⁵ newton, and one centimetre is 10⁻² metre, making one dyn·cm exactly 10⁻⁷ N·m. These units are uncommon in current SI work but useful when reading older material or instrument data.

Every conversion normalises to newton-metres and then divides by the target factor. Decimal.js carries all digits and the page rounds once at the displayed output boundary. The simultaneous breakdown makes unit mistakes visible: 100 lbf·in is 8.3333333333 lbf·ft and 11.2984829028 N·m.

A negative torque is allowed. The sign can indicate clockwise versus counter-clockwise direction under a chosen convention, so rejecting it would discard valid information. Conversion preserves the sign; it does not choose which direction should be positive.

Although torque and energy can both be written with the dimensional product N·m, they are not interchangeable quantities. Torque describes a moment about an axis. Work or energy is force integrated through displacement and receives the special SI name joule. This page never labels a torque result as joules.

The page also does not tell you how tightly to fasten a bolt. A tightening specification depends on fastener grade, thread geometry, joint design, lubrication, surface condition, target preload and manufacturer instructions. Use the published service or engineering specification. This converter is appropriate only after the required torque is already known.

Likewise, converting engine or drivetrain torque does not account for gear ratio, efficiency or losses. It preserves one stated torque in a different unit. Use the live torque calculator to derive a moment from force and lever arm, or a drivetrain calculator when a mechanical ratio changes the torque itself.

What is newton-meter converter?

A torque unit combines a force unit with a perpendicular distance unit. One newton-metre is the moment from one newton acting at a one-metre perpendicular lever arm. Pound-force foot and pound-force inch use the exact pound-force with the international foot or inch. Kilogram-force metre uses standard gravity, while dyne-centimetre is the CGS equivalent. Conversion changes only units, not the physical torque, sign or mechanical system.

How to use this calculator.

1. 01Enter the known torque, retaining any sign used for rotational direction.
2. 02Choose the source unit and check whether the specification says pound-feet or pound-inches.
3. 03Choose the target unit; the primary result shows that pair.
4. 04Use the simultaneous unit breakdown to catch a factor-of-12 or force-versus-mass mistake.
5. 05For a fastener, use the manufacturer's required torque first; this page only converts it.

The formula.

Assign every unit its exact value in newton-metres. Multiply the input by its source factor to reach N·m, then divide by the target factor. For 100 lbf·in, multiply by 0.1129848290276167 to obtain 11.29848290276167 N·m, displayed as 11.2984829028. Dividing the same canonical torque by 1.3558179483314004 gives 8.3333333333 lbf·ft.

The pound-force factors are derived rather than guessed: exact pound mass times exact standard gravity gives newtons, then exact inch or foot length gives the moment. This is why twelve pound-inches returns exactly one pound-foot before display rounding. All paths use the same canonical value, so arbitrary pairs remain consistent.

A worked example.

Frequently asked questions.

References& sources.

1. [1]NIST SP 811 Appendix B supplies force, length and torque conversion factors used to derive each unit.
2. [2]BIPM SI Brochure defines the newton and the SI derived-unit framework.
3. [3]NIST SP 330 documents SI units and the exact standard-gravity convention used for kilogram-force and pound-force.
4. [4]NIST Handbook 44 Appendix C documents customary/SI unit relationships used in legal metrology.